Never buy from CellC

I Would like to lay a full complain against this company. I paid off my account last year April after a huge fight with them I received a paid up letter. Few months down the line Cell see sold the account to MBD. After call I sent a paid up letter to MBD. The calls and messages still came though. I have sent email to CellC and MBD asking them to remove the account from the credit B it is still not done. A year down the line. This is to alert clients of what Cell C is capable of. How do you sell a paid off account to a collector, what if I did not ask for a paid up letter? And A year down the line, why is that account not removed off the ITC?