Failure of cancellation of payed up contract

I have bought a tablet on my cell contract in June20016,, Telkom deducted R99 every month until June 20017 when they phoned to asked if i wanted another contract. Said no they said i had to cancel with a form or at a nearby office. i live in a small village north of East London Went to town to there office. No they cant do it you have to fill in a form on internet and send it to ********** after several e mails and submitting the form they still kept on deducting the money. i phoned now there were curtain information that to be filled in on the form from them that they did not tell us about. We did that submitting it again 22-06-2017. Got the automated reply will be attended to in 21 days. Kept on deducting the money. in April 2018 no reduction and we thought well at last and they will refund the months of payment nothing happened. Yesterday they deducted it again!!!!! I just don't know what to do to get this canceled the contract was for a year now we are going to two paying double for the tablet. Could you please advice on this matter. We were advised to cancel the debit order at the bank with no success