Cell best at being bad.

Cell C is the worst company ever. I have had a contract with them and couldn't pay and they referred me to their collections agency NU Debt. It's been a year now since NU Debt confirmed I had paid off the account. I've been contacting cell c over and over to have this sorted and get myself cleared from Itc. Still today nothing has been done. They have been promising this and that yet I've never received anything from as they promised advising I had paid off. Any help from the public to help me Sue CELL C would be appreciated as I have lost a lot. I've app**** for credit and got declined as a result of CELL C and missed employment. I'm so ****ed at CELL C. Very unprofessional.