MTN Overbilling

On 15 Nov 15 I received a bill of R1800, I queried the bill and got the itemized statement and accepted it as I had used more than I thought. I made a request that the contract be capped at the 2gb that was the contracts allocated data allowance, I was given a USD code to type in that would do it for me, apparently. I used it and as a precaution I loaded 500mb data off my credit card, which showed a balance of 2.5gb, and made use of wifi for majority of my work on my device. Even though I did these things I still got a bill for R1700 the following month, which made no sense when I checked my Data balance, which was now 2.3gb (I have a dated screenshot). My question is 1: how can the bill be so high with virtually no data usage and 2: how could I have 2.3gb left if I went into out of bundle charges. <br> I queried this and cancelled my contract instead of upgrading, as it was already over the 24month. I was told the matter would be looked into and I would be contacted with the result. I was billed again the following 2 month for ~R250 and ~R110 respectively. The calls I made have been my only contact with MTN? The reference numbers are, ***, ***, ***, ***1-retention