Airtime disappearing when mobile data is turned off!

I called cell c today to find out why my airtime was being slow eaten up. the lady I spoke to logged a call and said I would get feedback, she also checked and agreed that it strange that 4 cents is disappearing at a time. I told her that I have not used the internet and turned off mobile data. I now receive a message telling me that my airtime was depleted on internet usage. How is that possible if I haven't used the internet or any apps requiring a connection? Also why would it be a set amount disappearing over the past few days? C'mon cell c catch a wake up. My mobile data has been turned off all this time, checking your systems can confirm this. This is clearly an error on your side. This type of service is terrible. How is this going to be sorted out and by when?