Payed off a bill months ago and now they come clai...

Payed off a bill months ago and now they come claiming I still have to pay collection fees! And sir on the phone said there was a system error that says in their system that I paid 1900 euros from the principal of 2500 euros while I have a letter saying that over 2500 euros have already been paid! bunch of mafia practices I take you to court.