Billed for wrong contract for past 6 months

I on 1 April 2015 upgraded my contract to UYO Minute _ 200 @ R229 pm but haven't received any of the minutes since then as per signed contract in my possession. Only realised when I walked into MTN Centurion Mall to enquire on my crazy monthly bills that they captured my contract as that of 3G Data hence I cannot make calls. I don't know what the hell happened that MTN would load and bill me on something different from what I signed for. I don't need 3GB monthly but airtime I signed for. I haven't even used their data as I was not aware I had such and have wi-fi at home. I've tried to write in to MTN but their confusing many and contradicting responses and treatment have been appalling. I have all of the email trails to forward. The 1st time they said they addressing the matter and send me sms saying their working on reopening my line and it will take upto 24hrs. The next day they send email to say they can't be held accountable and the next email said I must go sort my problem out where I upgraded which is 400kms from my permanent residence. I want MTN to correct this contractual mistake and refund me all the overcharges of since inception and give the 200 minutes I signed up fo