MTN doesn't respect us

MTN handed over the account to NUDebt, we adhered to arrangements made with NUDebt as well as their Legal department. We call these people to open our lines everyday. You only get them when you are lucky. We spend a lot on airtime trying to get hold of them since our lines cannot receive nor make calls. It is uncalled for and disrespectful. Right now we receive calls daily from NUDebt demanding money that we have paid. We waited 1 week for the money to reflect absurd because we paid in store, they asked to wait for 5 days to open the phones. We waited 2 weeks, and when we eventually get hold of them they saying lines were opened on the 24th Feb. But here we are 3 weeks later we still can't communicate