I doubt you were able to get diesel in your car, as the nozzle should be too big to go into your filler pipe..... Although BP do do an Ultimate Diesel!

This is a long shot, but there was a Tesco near me which had it's main unleaded tank filled up with diesel, courtesy of the delivery man, which in turn, led to a fair few repair bills coming Tesco's way!
Maybe this happened to you. I'd contact the petrol station in case anyone else has mentioned it.