Premature Cancellation

Good Day, I did move to Namibia permanently in Jan2015. I decided to premature/downgrade my contract due to the high costs of roaming. They did send me an offer but I never signed it and therefore the contract carried on as is. With the next debit order I did see that a similar amount was deducted. I did contact them again and they told me that I never signed the cancellation contract. At this stage I decided to cancel it in total and they did send me another proposal which I signed and paid and provided them with the proof of payment. I am still getting similar accounts as in the past with escalating costs. I have tried in vain via various emails and attached docs to find out what is going on. It is for me now n useless situation. Please help as this is now according to Vodacom to their collections department.