I had a similar problem, missed the payment cut of date, still not sure if that was because i wasn't paying attention or because of myunisa not posting it properly.
As soon as I picked up cancellation I went to regional centre(hoping to save some airtime). The staff simply told me that they were unable to help me. I asked whom I could speak to and ended up with the number they give you to make you go away.
I probably spoke to about six different people who all told me that there was nothing they could do even though my payment was only 3 days late...
Eventually out of pure desperation and frustration I broke down crying while speaking to some poor guy. I think he figured out that I was really upset and said he'd sort it out.
Sure enough after about half an hour the subject was back on myunisa!!!,,, so sometimes its unisux and sometimes unisa... I hope you'll experience the latter.
So just keep phoning and moaning and climbing up the ladder until someone helps you..