Frustrated with incorrect billing every month!!

Every month since I have had the wifi modem (October 2015) Telkom has either not taken money via debit order, taken too much money, taken money on different dates and now today has taken the installment twice via debit order. <br> <br> I have called customer care repeatedly to ask when the money is being taken, why my account (which was advertised as a fixed amount) is different every month & no one can help. Now today, two debits for R1045,36 went off. <br> <br> <br> I originally signed up for a R399 20gig a month deal (as explained by sales person telephonically). Then October no money gets taken, November R399 (which was correct). Then suddenly mid December an amount of R630 goes off. I told the bank to reverse that because my agreed date for telkom debit order is end of the month when I receive my salary. Then end of December nothing goes off. I called twice in Jan to ask when the money will be taken via debit. They explained that the billing is in fact not R399 -the paper for the account and modem are extra (yet to receive an account of any nature).R630 I can accept as Octobers installment with December. How was I to know this with no account and NAEDO debits mid month. Please refund my money.