Cell C charges data when you turn it off!!!! Please beware guys

Today I contacted Cell C's customer service center to find out why my account is very high every month even though I have 300 anytime minutes and 4 gb of data left. This does not make sense right?

So the lady on the other end of the phone explained to me that Cell C charges you data when you switch off your data and is not connected to any wifi networks. Can someone explain this to me please?

When I turn off the mobile data on my phone, my whatsapp, facebook or instagram does not work... It tells me "no connection"

That makes absolute sense, but telling me that those spicific applications running in the background uses data and that Cell C is not taking that from my active data bundles, thats a joke is it not?

Its pathetic and I swear to God *****ing!

Using data when you turn of your data and wifi, should I honestly believe it? ***!!!???