Overcharged TWICE on a signed contract

In January 2015, I app**** for the IPhone 6 contract with MTN. The contract cost was advertised and discussed with me at R499.00 per month. When I queried this with the consultants at MTN I even enquired if there were any hidden costs. I was told that I would only be charged R499.00 per month. If my data finished I would simply just need to top up. The first monthly installment my account was debited for the month of February and prorata for January - this I was understandable. But then at the end of March, R749.12 was debited off my account. I queried this with a consultant at the Eastgate branch and I was told that they found the 'glitch' and that my account would be credited for the next month. This morning I wake up and I see an sms on my phone saying that now R731.60 has been debited for APRIL. <br> I attempted to call customer care THREE times to query this, again. I sat on hold until eventually, the calls dropped. I am extremely unimpressed with the accounts department at MTN. I have other expenses to cover each month and I EXPECT an full refund for the overcharge for March and April within the next week.