Dispute billing

I took a R249 1gb free me contract with Telkom this year January and I was advised that my first debit order will be end of Feb, including pro-rata. My account was debited R488 end of Feb, which I had no problem with. Then comes the 8th March, I receive March invoice, remember it's not even month end, the invoice says R749 will be debited end of March. I went to the store where I took this contract, sales lady then advised I used R500 on the spend limit which no one ever explained that me, she then opened a case for me disputing billing on the 9th March. Today is the 26th March, my debit order date. I still haven't got any response. I gave been calling to follow up, my case is still not attended to. What must happen now?