Lack of clarity from call centre agent

First my 500 MB (contract) just vanished within 9 days when I ask the reason the response was internet from Simphiwe. Secomdly I asked how much are MTN is going to bill me in September the answer was R1 500, when I ask the reason the answer was Data. He couldnt even suggest to email me the comprehensive invoice. I ended up cancelling the contract, but I wanted to upgrade. my avegerage spent is around R179 the highest was the recent of R270, just towards the end of the contract the bill is R1500. <br> Thirdly i bought data on my prepaid for phone 150 MB, three days later those data vanished, can someone explain what is going on.