MTN took what does not belong to them

I went to MTN Irene Mall last Saturday to find out what I need to do as I wanted to port my number back to Vodacom. The agent suggested that I convert my package to Pay As You Go since my contract has already expired. I completed the form and then enquired about what would happen to my airtime. She indicated that I would loose it. As I had almost R300 of airtime, she suggested that she holds back the form, I use the airtime first and then give her a call to submit the form for processing. I told her that I would be out of the country and that I would only be able to attend to it later this week. This morning I just received an SMS to inform me that my balance were reset. So suddenly I have no airtime left, which I planned to use today. I haven't given the instruction to MTN to proceed, they just went ahead and did it!!! I had about R160 airtime left. I tried to call the shop a few times, but no one bothers to pick up the phone. I want my R160 airtime back!!! MTN this is poor customer service and taking airtime back that I have paid for but not used is *****ING!!! So please make a plan to get my airtime back to me. You converted my package prematurely before I gave the go ahead!