Botched upgrade and no service since then

I was called by Buy Mondo to upgrade one of my Vodacom contracts. To cut a long story short, they upgraded the wrong contract. I cancelled it the next day No feedback from Mondo since then - I have called repeatedly and waited for ages only to get cut off. My email from 4 days ago is still not acknowledged.

So what now? Where do I get confirmation that the upgrade has been cancelled

Terrible service!!!