Charged without my knowledge

My boyfriend lives in England and we chat on FB messenger constantly. When I called him from FB messenger, a notice came up before the call was made to ask what data I would like to use... Surely if I receive a call I shouldn't have to pay, an incoming call does NOT ask me what data I would like to use so in other words I'm not paying for it. Cell C calls me yesterday and says I owe them over R2000 in data, I'm sure it's from receiving FB messenger calls BUT I WASN\T THE ONE MAKING THE CALLS and no notification came up to tell me I would be using data. I'm ready to take this to court! And changing my network as soon as this contract is done - I am sick to death of Cell C"