Items on slip that wasn't asked for

Went to BP in Village Road, Johannesburg this morning, and was billed for a Vodacom voucher I did not ask for or buy. I didn't realise this until I got to work, which was obviously too late to go back then again to complain. This is the 2nd time this has happened where I was billed for an item I didn't request. The cashier Patrick didn't even bat an eye when he passed me the till slip, knowing very well that I didn't buy the item, but I paid for it. How many other customers do they charge for items not being asked for? And what happens to the extra money? Do they report it to their bosses at the end of the day, or is it being pocketed by them? And the best is, I don't even have a Vodacom number, so then why would I even buy a voucher for Vodacom.