Money taken without any explanation

The biggest mistake I've ever made was taking a Telkom contract, which i don't even use. 1st I had major issues sorting out the billing, which it appeared they were debiting some other poor persons account. Finally that got sorted out, with them editing everything and taking the back dated amount from my account. Everything went well after that, I was receiving my statements and the amounts were coming of as requested. However on Friday, my account was debited for R499, which makes no senses, not to mention that I had received no communication of this. My contract is for R149 so where this random R499 comes from is beyond me. Further my statement indicates R149 and that it is up to date. I am going to get my bank to reserve this amount as I received no communication about this. This is utterly ridiculous. I actually want to stop all transactions because it's sicken that Telkom can just delve into ones bank account as and when they please with no explanation as to why. And when you try to contact them it beyond impossible, with their online chats not working, facebook requesting that you do it another way. Holding on the call lines. Pathetic service.