None taken at all. I used the word 'bank' as that is the word the OP used. I would go back to the orginal 'institution' that held the original debt that was supposedly paid off for records of that debt having been paid off. I don't think I would rely on the bills having stopped coming in as proof it was actually paid off. I will admit to not being familiar at all with all this buying of debt business - but could it be possible the second 'institution' received the OPs money, didn't pay off the original debt but rather just negotiated to buy the debt from the original 'institution' and kept the OPs money (which would stop the original bills from coming), and is now going after him again to settle the purchased debt? Which would all sound highly irregular to me - but an 'institution' only having 12 months of records or not being able to produce records sounds irregular also. What about records of the OP having paid the second 'institution' in the first place? Kind of a confusing setup.
Nice work...you're learning quick.
these "debts" are bought and sold like used cars....and guys that were too rough for the used car business are hired to "collect" or recover the new owners asset.
they may not have paperwork prior to the 12 months because all they buy is a debt( not sure on that though)...not a debt history. they are not here to make Nice with the debtor, they are here to make money. no harm in that as long as everybody knows the games rules.
Your "debt" can be someone else's "asset" once sold as such. Money is a lot of fun to learn about but most people don't take the time or feel its not necessary. its not rocket surgery....or porting a saw....or chain filing