INCORRECT CONTRACT LIMITS LOADED

I recently upgraded my contract in April. Went from having a top-up contract with my Blackberry Z3 to a top-up(So I thought) contract with my new Samsung S6. Unbeknownst to me an ADDITIONAL credit limit of R1000 was set on my account. When I first started getting SMSes about this and queried it - I was told this was regarding my premiums and that I need not worry. When my line started getting cut and my premiums went up drastically I tried called AND going to the service centre directly but then MTN was on strike for weeks. I went into the service centre again end of June and found out that my contract was incorrectly loaded and was not top up but they had added an additional R1000 credit limit in the background?! This IS NOT what I asked for and now I have huge amounts outstanding!! When I went into the store - I had to pay R 1 740.00 just so that they would not suspend my account YET AGAIN!!! During the months I purchased several data bundles and was under the impression that I was ONLY using the 300MB that I get a month along with these bundles I was buying and did not know that I was actually using this SECRET credit limit. Dushen is not giving feedback as promised - hopeless.