Disgusting service

I had a contract phone for 2years and on the 22month I emailed Vodacom that my contract is ending. They never rep**** and kept on deducting even after 24months and I reversed my money. I eventually wrote here and they called me asking me for proof of emails which I sent. They told me I am liable for the R800. Which I refuse to pay because I have proof that I have made contact with them to cancel my contract. I'm now in arrears and owing over R1000 because I refuse to pay money that I never owed them. My worry is that I will get blacklisted. I still refuse to pay them as it wasn't my fault they never rationed my request to cancel the contract. I gave them proof they never even acknowledged my email other than sending me monthly statements of owing them.