Extra premium

I have a contract of R700 with Telkom, the first month they debited r1000 from my account and when I enquired I was told the extra money was pro rata. the following month they took another r1000, I called their customer line I was told a pathetic story and I was referred to a branch, when I got to the branch they also couldn't explain the r1000 I then went to reverse it. then this month end they took r1600 and I was told if I don't pay on a certain month, the company adds r200 on top of my next debit. but now when I go to the store to get answers they cant give me and when they also try to call the head office, no one answers and still no solution for me. they keep increasing my premium monthly without any explanations and no one to give me answers.