Kellogg Canada Inc. Kellogg Gas Cards cannot be redeemed Mississauga, Ontario

Kellogg has a promotion where it offers Mastercard Gas cards when you buy certain brands of cereal. You order the card using the info on the cereal box. So far, so ggod. You get the $5 Gas Card which you must activate.  Seems to work.  What does not work is finding a gas station that knows how t0 process these cards and will accept them. I have sent e-mails to the company that administers this program for Kellogg and they are unable to give me the name of a gas station that will accept these cards.  I have also sent Kellogg 2 e-mails on this issue but am still without any response.  In conclusion, I have in my hands 3 of the cards, total $15, which seem to be worthless.