Cell c

I will never advise the anyone to take a contract with cell c they handed me over when i was paying them then when i was busy paying the account this year i got a call from norman bisset that the account was sold to them but still it shows on my credit record i owe them 3000 ive tried calling them even their legal department send emails no one is getting back to me. If the account is handed over why does it show into my credit account because it doesnt belong to them anymore