Telkom gives headaches more than service!!!

My contract with Telkom came to an end last year January. I made payments on their portal in December, both for December and January. An invoice, with "final invoice" written across was sent to me in Jan with a credit balance of the amount due for January. That was supposed to be the end of my dealings with Telkom on this contract. However, Telkom decided to debit my account for monies that had already been paid and acknowledged by them. They now want me to pay them R207 which has accumulated interest, for debiting my bank account for funds already paid to them. Really!!!!!! This morning, I received message of a trace arlet loaded by them to the credit bureau. I feel bul**** by Telkom, which is totally not acceptable.