my gig of data depleted in 2 days

i have a contract with telkom , in 2 days from the start of the new month my data was depleted and when recieved the log on all that had happened on my account i noted that data charges were taken on my cellphone when i wasnt even using it *all background apps are off and restricted by me* when i called i spoke to 2 agents , the one lady dropped the phone and another gentleman by the name of Karabo Tjale could not give me an answer as to why these big charges went of on my phone and all my data depleted when no apps run on my cell except my whatsapp .. i recieved the statement of usage here which makes no sense at all ... i was charged when connected to wifi and im on airplane mode ... i need a clear response as to why this happend