over chargers

Dear Sir, my name is Mrs Singh mtn no ***. I have been billed an amount of R3344,94 in april 2015 and R3530.18 in sep 2015 for data that I have not used. I have requested credit but to no use. I have 60 gig data at home and a blackberry unlimited data so Y for Gods sake will I run up a bill so high. The both times are when mtn had a wage dispute and in sep when Mtn nigeria had the fines issued. I am not a person who is on the phone all the time. I have a business to manage and I carryover data and airtime everymonth. I also have in writing from mtn that I have to have a limit placed at the branch so that I wount exceed my limit which I do. I also have a limit on my phone set and call 141 on a regular bases to ensure I don't exceed my limits. I have requested a detail listing for the sites and duration on each which I didn't receive. I have a business to maintain and its difficult without a phone bse they suspended my services. If they insist I can pay R10 a month bse business is very bad and I have not used that data. Awaiting your reply. You can contact me on *** kind regards