Being harrased over paid cell c account

I use to be a glocell customer. Glocell customers have been handed over to CELL C, however my outstanding bill still had to be paid to glocell. Now I am being threatened by having my service suspended by cell c because my account was not paid to them. This is very unprofessional. Surely you guys should have sorted this out by now. If this matter is not resolved urgently, I will have to go to the celular umbutsman with this matter.