Deducting account even after I cancelled contract

I've recently contacted Voda Com and requested a settlement amount to cancel my contract. After receiving the details requested, I immediately paid it in full. There was an outstanding amount which I also settled. I have all the proof and communication. They requested I complete a form to indicate if I would like to keep my old number or forfeit it. All this was done and email to them. I kept my number but chose to continue on pre paid which I will buy my own airtime. With the new month I didnt receive my airtime(as with my contract, and thought it is all sorted as my cancellation went through, That was not the case, my account was still debited with an amount of +-700 rand. I immediately reversed the debit from my account which stated my arrears. When I phoned in to the call centre I was transfered from post to pillar, everyone telling me a different story. Transfering me from contract to pre paid and then to collections. Waiting for almost half an hour. When I finalliy got to the collections department i could hear someone picking up the phone but chose to make as if they cant hear me and drop the call. This is disgusting service from 1 of the most popular brand names in SA.