Moved to the UK, cannot get a response to cancel contracts

Trying to end my contracts (that have expired in July) and downgrade them to PayAsYouGo (I'm returning to SA and want to keep my numbers) seems to be an impossible process? I'm living the UK and my first option was to call the cancellations department - after spending over 45 mins on an international cellular call on hold I gave up. I proceeded to use the MTNActive portal to submit a cancellation request as well as their website link requesting the same. It's been a month later, no response and I'm being billed over R500 per month on a contracts that I'm not using :(