Blacklisted for a paid up account

I had a cellphone contract with Mtn of the contract was paid up in March 2018. Two months past and they started deducting again and I reversed the payments twice. In October I received an email to contact the legal dept I went the store in Cape Gate where I took out the contract and they could not assist me. I than app**** for an account just fins out they have blacklisted me. I received a credit report and there it still shows they did not clear my name as the legal department said they would.