False pretenses

Bp ran a promo where you would get vouchers for collectable cars if you spend a certain amount for a number of times. My son got into this and collected 3 of the 6 cars. That is due to no one having stock to provide him with cars for the last 3 vouchers I got that got wasted. It is really disappointing and we feel we went out of our way to go to a bp for no reason. They are not an honest organisation.