Cancelled contract with outstanding funds?

I had a 2 year wireless wi-fi modem contract with Telkom, for which I was paying R279 a month for two years. My contract was meant to end in October of 2015, but I wanted to renew or continue on the existing plan I was on. Telkom did not inform me that after my contract had ended, they would be charging me R547 a month for the same amount of data I had been receiving during my contract period. Ironically, I received an invoice every month prior to this, so I was able to see how much I was expected to pay. When I did not receive an invoice or any sort of communication from Telkom I decided to visit a branch where I was informed that I was owing R500 for that month's contract. I refused to pay that amount and requested that my contract be immediately cancelled, which the consultant affirmed. A few months later while applying for a loan, I was told by my bank that I am listed on the Credit Bureau for an amount of R746 owed to Telkom. I immediately called the call centre where an agent advised me that my previous case had been unresolved. Is this the kind of service we are paying for, Telkom????