MTN REFUSES TO ASSIST WITH INCORRECT BILLING

My son was a Nashua Mobile customer and was extremely happy with them. Unfortunately they closed and his contract got move, without any sort of signature, to MTN. Since then MTN have been billing him for a Blackberry plus BIS and caller line identity with a R350 monthly top up. Problem is that this Blackberry contract was upgraded mid 2014 where my son then got an iPad Air with DATA. We have visited MTN Richards Bay where they updated everything for him yet nothing has changed on the billing. When emailing I get told not only does the Nashua Mobile contract from 2012 state a BB but also that I, as a 3rd party, am not good enough to deal with. They refuse to look into why, when we traveled the 100km's to Richards Bay and back, nothing seems to have been noted on the system despite the person there entering everything my son told them on the computer. MTN also wants some MTN pin??? He was a Nashua Mobile customer. What MTN pin? Even if my son does email or phone himself, he has no idea about any pin. MTN further asks for the contract which we do not seem to have a copy of. Surely they should investigate from their side together with whomever handed over from Nashua Mobile???