Bad service

I moved homes and contacted Telkom to move my line after months of waiting i cancelled my contract with them. Started getting calls from Blake and Associates, i rep**** that i cancelled the account months ago and they were still billing me. They eventually asked me for proof of cancellation which reduced the outstanding amount. Before they start harassing people for money, Blake and associates should first check to see if their clients work was done properly. I paid the amount and asked for a paid up letter, and for them to fix the error on my credit score. No response to this day and im still getting a invoice from Telkom.