cheated out of data by mtn and wrongfully charged

End of April I recieved a HUGE bill from MTN for the month of april and march 2015. Apparently I used R3100 worth of internet after I Purchased my 1 Gb. I tried to sort it out with Mtn but they were on strike till middle july. Every day i take a screen shot of my data after dialling *141#. According to mtn on 5 April i did not have any data but according to my screen capture I had 710.90 MB of data.. On 11 April when my month ended I had 383.13MB. On 12 April when my new month started I had 716.20 MB data. When you deduct the 2 amounts it is 352MB, and i recieve 350 MB every month with my contract. 4 Requests have been logged with MTN and they refuse to fix the problem the say i must pay the money. I feel it is wrong of MTN to treat a customer that way, they are *****ling my money. My line gets suspended every monday from the 14th May and i am getting fed up now. never have i exceded my gb i purchase every month till now.