INCORRECT OPENING BALANCE QUERY

I used to be a Nashua mobile customer , my contract was taken over by MTN. Two months in , they give me a payment due of R1910.00 after I have just paid my monthly instalment. After trying to get through to the call centre with my call being dropped numerous times, Eventually you are put on hold for 30minutes to an hour before a call centre agent answers your call. They advised me that the amount due is an opening balance from Nashua mobile, this is impossible! I supp**** them with the statement I received from Nashua mobile were it shows R0.00. Still the amount has not been reversed two months after I have queried. I have placed a complaint on hellopeter to have someone phone me promising to do the best to have it resolved , this was mid May. Now today they have yet again suspended my line. Now I have to pay R900.00 to have my line reconnected, and IF & WHEN they fix the query they will credit my account. So I must pay money that I do not owe just so that they can reconnect my line. This is Ridicules! In the mean time my profile is being affected negatively because this query is not being resolved! I REFUSE to pay money that I do not owe!!!