MTN overcharging for agreed contract

MTN subscriber through Nashua Mobile and migrated to MTN Direct when they closed. My contract with Nasua expired Dec. 2014. I contacted MTN to be changed to prepaid and was told that I had to take a contract and a new phone. I did not require a new phone so requested only the new contract at R 39 monthly IN TOTAL. It was called something like \my choice"or similar - the most basic contract possible. It was to be set up with a zero usage limit.<br> Jan.& Feb 2015 account was R 90.18 and was Feb. R 90.18. I queried and was told that this was still the Nashua contract (expired Dec.). I again requested the new contract and it was confirmed that this was in process and that I would be sent a sim card which I wouid have to accept even though I could continue using the old one in my existing phone. Mar acxcount was R 160.86. Queried and told that there were once off upgrade charges. Now I see April account to be charged is R 149.67!!!!<br> I am a pensioner and specifically requested the cheapest"