Paying for free services under contract

I have an Anytime 200 contract with MTN, via a corporate client (Aurecon). Since the start of the contract in June 2015 I experienced the following problems which have been reported but not addressed yet. Figures quoted below are as per December 2015 invoice though similar figures for previous months:<br> 1. Calls - Only the first approx. 20 minutes of my calls (200 minutes) are for free, thereafter I pay. Total call duration was 150 minutes but I was billed for R262.<br> 2. Data - 500 Mb contract but only approx. 120Mb of data was free . My total usage was 303 Mb, still within the total contract of 500Mb but I was billed for R155.<br> 3. Accounts received reflect only payments for last 2 months instead of 6 months.<br> 4. Statement wrongly reflect credit of R204,000!<br> <br> I must admit I had a MTN 350 contract before for 4 years without any problems!