Useless support staff and mystery data

I get the SMS's from Vodacom stating that I've "used R0.50 out of data bundle so far this month", and urging me to buy data. Seeing as I only connect to the internet via wifi, I know for a fact I haven't used any.

So I go onto Vodacoms website and use their chat feature to try and find out what is going on. I get put through to someone named Lulamile who gives me the Spanish inquisition 'to make sure it is the owner', like anyone else other than the owner would care. I didn't know the tarrif name, or whatever that is, so she said my answers don't match what they have on the system and hung up on me. I tried to chat again, and she wouldn't answer any questions. Clearly didn't feel like doing her job today.