Terrible Service

I am so fed up with Telkom and their shoddy customer care. My 2 year contract came to an end on the 16/12/2015. For 22 months I have been debited the contract amount of R149.00 for a Wi-Fi device and 6 gigs of data. Then all of a sudden I am debited R297.98 on the 30/11/2015. I tried to query it by emailing the retention officer who contacted me. She said she will get back to me. After a few more emails she said that its because my contract is ending and these were prorate amounts. Then at the end of December I am charged another R367.00. I again tried to contact them to no avail. Low and behold I am charged another R95.00 at the end of January. What must I do to get Telkom to stop helping themselves to my bank account.