Vanishing Data and Airtime

This morning (21.08.2017) i checked my data balance to see how much i had left, and i saw that i had a little over 700MB left, then at 19:58 i get an sms stating that i had less than 67MB and not long thereafter it was depleted... Later the evening i purchased myself a R70 airtime in which case i then converted some of it to data 250MB to be specific, which did not even last me a minute, then i received an sms again sayin my data has been depleted... I wanted to convert some of my airtime left but then i had insufficient airtime as well...

Can someone please explain to me what the ell has happened to my data and airtime and where the hell it could have gone to in under 5 minutes time and all i tried to do was send a whatsapp message...

Please don't give me some ridiculous story about other apps running off my data as the bulk of my apps has been set to wifi and this is the very first time something like this has happened and i need answers and my airtime and all of my data back...