Appalling Service With Regards to Contract Cancellation

I cancelled my contract in a branch, and asked that they provide me with all the monies outstanding, as my mother had passed away and her bank account had frozen, so I wanted to get the account settled and paid up, so that it was one less thing to worry about.

My account got handed over to the debt collectors, due to non-payment of the cancellation fee. There was no cancellation fee mentioned when I was in the branch, as I was given the impression that the contract was paid up and cancelled. They didn't even have the courtesy to give me a letter of final demand to try rectify the issue.

I have now been pushed from pillar to post, because according to the branch and the Customer Care line, the contract has been cancelled and is prepaid. But the debt collectors are hounding me for this money, that I cannot even confirm is truly owed.