It so happens like my Mom got a letter from the Indian Overseas bank or IOB, two years back, informing of a Fixed deposit that has matured which they are automatically renewing. My mom tried to search for and think of when she made that fixed deposit some 10 years back and where she kept the original certificate of the deposit to claim it back.
She approached the bank, which requested her to search all places where she might have mis-placed it.. because without the original certificate it would be difficult for them to process it. My mom had agreed and over the next few months, in about 3 months she searched over at many places, including her ancestral home in her native town when she went there for a relative's wedding.
She couldn't find the originals.. She approached the bank, which said that it can provide a duplicate 'original certificate' if she filed a banker's bond document requesting for it saying she lost the originals at a cost of 250 indian rupees.
It so happens that, She made the request, got a certificate, and also the amount of the deposit on its maturity.
Two years after this, Yesterday, she gets a call from the bank saying that it wasn't her money, that they had processed it by error.. and the original depositor has approached the bank for the money with the original certificate.
They said.. 'We are calling up to notify you of this issue.. and request you to check your documents on this.. and we will call you again in one hour'..
My mom immediately recollected that it is why she could never remember anything about the deposit, and neither find the original 2 years back.. she waited to see what the bank tries to tell her in their next call.
The called to say that they would expect her to visit the bank and possibly re-credit the amount back to the bank.
It seems the original investor himself has been the bank's manager 2 years earlier. At the kodambakkam branch of IOB. And that he had deposited this in the name of 'Uma' which was his wife's name. Since my mom's name also happens to be Uma, the bank had sent the intimation of the renewal to the wrong address and lost record of the original investment temporarily (or permanently).
My mom consulted a relative who once worked in IOB, who told her that sending a wrong intimation letter can be understood as a clerical error, but they have went aboard to wrongly give the money itself to you, which is totally ridiculous.. and dont pay them unless you get it in writing from them that they made a mistake on this and are requesting a re-credit.
By common sense, most of us would say, the bank will never a letter like that confirming on its handling of the money which could be used to dis-credit the bank publicly.. and neither they can sue my mom because that would also prove they accept the error.
But my mom also had a point that they could try to make this a mistake on us by trying to screw up with other relationships I have with the bank in my savings account or other accounts in future... and my mom prefers to recredit the money back to the bank because she understands now that the money was never hers as she doesn't remember making any such investment, and she only had to believe it otherwise because of the bank's letter.
The amount was small.. 33.5 thousands and I told my mom that she is deciding to give it back only because the amount was less and she wouldn't if it was some 2 lakh indian rupees.. to which my mom quickly adds 'if it were 2 lakhs I probably would not have believed that letter at all firstly.. because I never had that kind of money to deposit then'
Whatever.. this episode proves how badly IOB is capable of goofing up.
Another similar episode:
This has happened in the Kanadukathan branch of IOB which is Kanadukathan near karaikudi town, some 10 hrs drive from Chennai.
My mom went to the kanadukathan bank to check on her account and stuff.. while she noticed the manager of the branch has changed. She came back home and asked her father (my grandDad) what was with the old manager who was a nice man and was there for almost 4.5 long years.. (it seems IOB managers are transfered only once in 5 years)
My granddad has narrated the below episode.. as reason for the manager change.
It so happened that somebody who had taken a jewel loan at the bank, came back to repay the loan and take the jewels. While the repayment was processed and jewel furbished back to the claim processing clerk who returns the jewellery, in those few minutes between the time when it was going to be handed over to the customer, the jewel got stolen.. The bank claimed that somebody who was at the branch that time had taken it.. these were old days and even these days IOB only have surveillance cameras in its branches in cities, not lesser towns/villages.
The guy bluntly said he wanted his jewels back and not its cost. This issue got on for a while as a disagreement when the bank chose to informally settle the dispute with panchayat like meeting with the branch manager, some of the clerks, the customer, and some outsiders who were influential. It was forced upon the customer that there is no way they could get back the jewels, and so he will have to take the cost value of the jewels. Also it was forced upon the manager that he bear the cost from his personal money because neither the bank can blame anybody to take up the responsibility or pay part of the amount, nor they could open-up on the lost article because it would discredit the bank's way of handling it.
More so, I think IOB managers decide things based on the cost of it and put the cost to the bank.. they write it off... except strange cases where the manager takes ownership of the error.
And so it happens that the manager paid up the 60 thousands from his pocket, and subsequently requested an immediate transfer from the branch because of the episode.
I ended up paying them online, only because they were using a 3rd party online payment services provider which I trust. After I made the payment, I read that the subscription will start only 4-5 weeks afterwards'.. uncomfortability begins again. 
