No way to enter the competition fairly

BP has your bundle of Joy competition on but when you try to enter with your slip they keep telling you the slip is invalid. How is that a competition if they have a computer sending out messages that says this. We only use BP to fill up so I wonder what slip they think we are sending them. So now we can’t enter because it says we have already entered the competition after 5 times of telling us the slip is invalid. Here’s my question has the forecourt guys entered our slip. I wonder if this competition will be fair at all if that’s the case