Deduct money from my account without permission

For the last 2 months I have received poorly service from Metro Fibre and the client service is pathetic! I've ask Metro Fibre about my invoice that is all of a sudden R850 and I've been paying R760 for almost 2 years now. Then they are trying to deduct money from my account without my permission. I've ask in December to fix the problem and nothing has changed! Now it's January and still my account is R850 but there was no communication regarding my account that has gone up. And they are fast to tell you that there is an outstanding amount but pathetic to answer the questions I've been asking since December. Real pathetic service , no wonder they have 2044 negative reviews!