Debit orders still put through after contract cancellation

I had a fixed amount contract with Cell C for R99 per month for 24 months. Not only did they put through any strange amounts, ranging up to R600 some months. I also sent contract cancellation emails to: *** to *** and to *** after my 24 month contract was finished. They still deduct money from my bank account. I reverse, stop and query the debit orders and Cell C simply uses a different reference number and put through the amounts on my bank account again!!!!! NO ONE answers a phone to cancel contracts or to complain, so getting hold of somebody that can assist is impossible.

I want my contract cancelled and for Cell C to STOP putting debit orders through!