Final demand issued without details

In October last year i received an e-mail demanding payment or legal action would follow - when i followed this up i was told that this e-mail had been sent in error as all my accounts were up to date - no apology was ever received from the accounts department -the branch however did send me an e-mail apologising. Now i have received another final demand for payment and once again no-one can verify what this is for. This sort of service is unacceptable - if you are threatening to sue someone for outstanding monies at least have the decency to put the details on your correspondence. Why is is my reponsibility to now follow up and go through my accounts one by one so someone in the accounts department can verify why i have received this letter. I requested a letter stating that this had been sent ONCE again in error as I was told that ALL my accounts are up to date and till now have received nothing (once again).