INCORRECT BILLING

I bought a cell phone from Nashua mobile in 2013 November Samsung galaxy S4 the service agreement that I signed for was R379 monthly instalment for 24months. They were billing me for BIS R58.99 since the inception of the contract which I never notice since I wasn't checking my statement on a monthly basis and again in august 2014 they added another service without my request for 2 G Data bundles R245. I started to enquire about this late last year when I checked my monthly invoice, I notice that in was paying more than R700 per month. I then contacted Nashua about the incorrect billing they said I'm responsible for that I should have informed then immediately I receive the invoices. Nashua only did a credit note for BIS and they said they are no longer responsible for my contract I should contact MTN. November 7 2014 I started communicating with them a consultant promised to fix the problem before MTN start billing me, since then I have been calling their office for help until today. February and March 2015 I decided not honour my monthly instalments as was tired of being billed for services I never requested for. MTN suspended my service without helping me.