Airtime theft

Hi there. I purchased R50 airtime on Wednesday. Used R20 to buy data and I was left with R30 airtime. Mind you, I didn’t have make calls during this time and yesterday when I checked my balance, it was R6. The extra airtime is untouched and I haven’t called anyone. Today I checked my balance and it’s R0. My airtime keeps disappearing and this makes NO SENSE! I’m not using data, I’m on my WiFi so it’s not even a case of my mobile data being on. I’m so upset and I feel **********!