MTN BULLING TACTICS

MTN called late in August for an contract upgrade a day I went for it beginning of September. Then after upgrade MTN continued to charge for old and new contract together. First time I queried it I was told it is system error and it will be fixed next month.Next month it wasn't and then this time was told it was once off then the 3rd month was told it how is supposed to be like that and someone who assisted suppose to have had told me. I think MTN just bullying me and making me pay for something they cannot explain themselves. The thing is if was told had to pay for 2 contracts then would have had agreed with what so called upgrade. The only thing they good at is to give me endless ref no.s and not resolving my concern. Their last ref no. was *** and they told me is closed?