Vox telecom - absolute idiots

Absolutely appalled with their service. I moved from Cape Town back to Jhb last year and cancelled my subscription. First they confirmed it, collected router 2 weeks later than agreed upon but it was sorted. Then in Jan I get a mail saying I owe them money - I send them their mail confirming cancellation with the correct notice period which they apologize for and send me another email confirming I owe them nothing and it's a system error on their side. Now I'm getting phone calls from debt collectors saying I have to pay them!!!!!! I have never in my life had such idiots to deal with. What must I do now???? Send them the emails AGAIN where they appoligise and THEY agree I owe nothing???? This is rediculous