Bad service false promises charging us more and more with every call

I have now had it we had pricelock which finished on the 31st Dec bearing in mind we paid it upfront for the last couple of mo months with the promise from them that we would get 2months free i have written proof of all i have screen shots in the beginning of January we were in credit with 750.00 now on the 27th they put a debit order thru for R3834. 00 where in God's earth can a dstv account go up from a credit of 750.00 to a debit order of 3834.00 in 36 days i really need clarification as i am still waiting for my 2free months i have gone to there local offices here in East london I have spend hundreds on cell phone account and still no answer just a dead decoder i really am in dismay.