Being charged after contract terminated!

So in March i had an issue with MTN that i posted here. They couldn't terminate my contract timely due to them having technical problems at their call center for more than a week! I was advised not to use the services until the problem is resolved and my contract is terminated. I was to be migrated to pay as you go and invoice reversed. I obliged and eventually the contract was terminated and airtime, data and sms bundles taken away. <br> Then they still debited me R717 for that invoice! I reversed this through my bank. I called customer care but i can no longer get through to contract customer care due to being on prepaid. I kept being returned to pay as you go customer care who say they cannot help! Since then i keep getting messages that i owe MTN and if i don't pay my services will be disconnected? ***??? Haven't you put me through enough grief with this? Customer care via email and your twitter account is non existent! Never get responses, ever!!! In one of the messages i now owe R728, then R739, then +/-R1340! Fix this mess and stop bothering me!!!