Charge on a terminated contract

I left SA 15 months ago but religiously kept paying my data contract right up until its termination date. 2 months before the end I gave Vodacom written notice to cancel the contract completely and to not change the number over to a pay as you go number as I was obviously overseas. I received a final account which was a little less that usual at the beginning of November (the contract ends on the 22nd) which was paid. In the last week I received another account for another full payment! Surely I am not paying in advance for December? I mailed Vodacom customer service but of course no reply. They say call the customer service number toll free..... unfortunately it is not 'toll free' from the UK! So please Vodacom. Get this sorted..... Mobile number has a +44 in front of it as no one seems to be able to find me?