MTN poor service

Dear Peter, I was indepted to nu dept management where I had to pay months that was lapsed and I payed R3500 to close the cellphone account. I called nu dept management to conform and send them proof of payment to close the account which they referred me back to MTN saying I must send an email I did and nothing happened, when I call they say not even a single payment Made and I still have the slips , nu dept is not even taking my calls and MTN does not want to cancel the contract as they said they will.