Billed after contract cancellation

I had missed 2 months of my contract payment, then I made an arrangement with Vodacom to catch up and to cancel the contract as it had reached expiry date. The consultant agreed to cancel and put a debit order in place for the balance until 20 August. All the payments went through as agreed and then after the 20th of August, I received a letter offering me a discount on the balance of my account. I queried this with Vodacom collections department and they advised that the account was closed on their side. I contacted customer care and they said I should call the billing department. I called the billing department and they told me that the account was still in force and hadnt been cancelled. I explained the whole story to them and told them to check their phone records as I had requested for cancellation. I, again followed up with them then they advised me that the account is now with attorneys. I immediately contacted the attorneys to find out why my account was with them as Vodacom was not shedding any light. They only responded to me today offering me an out of court settlement. FOR WHAT?? My account is paid up. Vodacom cant even produce a billing statement to show where this additional amount is coming from. I refuse to pay this as I terminated the services long time ago. Its not my fault that their own staff did not cancel the contract as instructed. THIS IS ****************!!! Not 1 person from Vodacom has ever called me to assist with my query. I am disgusted!!! And this is obviously going to affect my credit record negatively!!! Nxa