Telkom poor service

We had an agreement with Telkom that I will pay R200 for their 80GB day 80GB night so last month they debited R328 when I call them they told me that they borrowed me airtime and I used it that is why they debited more money and this month they will debit R644 and no one told me that they gonna borrow me airtime or ask ifdo I want them to borrow me airtime. So when I saw airtime on my sim card I thought it's part of the deal because no one explain to me from the day I was signing the contract they should have told me before I sign their contract their service is very poor they make us sign contract without explain everything to us the next thing they debit more from our account the are ********