Airtime dissapeared and no response form Call Cent

I recently got an mtn number. Today I recharged my account with R15 at 09:12 and I have the sms to prove it. I made a call which lasted less than 2 minutes and the phone cut. When I checked my balance it tells me I have R0.03. My question si how was it possible to deplete R15 airtime sooo quickly? I am not getting a response from the call centre-it gives engaged tone and I have been trying since 09:12 to call them. I have over 90 MB of data so it could not have been depleted by the data. I was reluctant to get an MTN numebr and now that I have I am having regrets. Can MTn please re-imburse my R15 airtime?