Inconsiderate Cell C service provider

Worst service provider ever. Contract has been closed and the total due of R511 paid up. They still hand over the account to MBD for collections. I sent them proof that the account is settled but still the account is not settled. I sent Cell C to their customer service no response from them. The account is still open under my credit bureau and now shows as I am skipping payments. I didn't even renew my contract because of their incompetence.