MTN reserved my airtime for no reason.

I purchased airtime for R60.00 and when I check my balance it says R32.50. I phoned 173 and Lindiwe said my actual balance was R72.50 which means the R 40.00 was reserved for internet not sure why since I have wifi at home and at work and my data is always off since I don't use my phone while driving don't need to switch on mobile data. Was asked to switch off the phone for 5 minutes which I did and later the balance was R72.50 and 10 minutes later it went back to R32.50 phoned back and less interested guy was put me on hold. I phoned back again and spoke to Lindiwe who said my mobile data was on and internet reserved it. All I want is my airtime so I can finish it before potting my number to Vodacom.