AIRTIME GRINDS!!!!

I have currently bought over R300 airtime in the last few days and I always buy power bundles in order to save. I have been very annoyed that my airtime gets depleted all the time. I am not happy with your services. For example yesterday I bought R30 airtime in the morning, I bought 60mb data for the day then later that evening I wanted to make a call and my airtime balance was at R0.62 mind you I have not made any calls except buy data for R6 and send an sms. I am not sure what is happening because when I was on contract these things weren't occurring. I M very angry about what is happening. Please do assist me with this problem. Thank you