I signed papers on a new car at toyota and before i was out the door they say they cant finance?

I was recently approved at a Toyota dealership for a new 2010 Prius II. Even though about 3 1/2 years earlier I had filed chapter 7 bankruptcy & I've been self-employed for around 3 yrs I still scored in the low 600's so they told me to get a co-signer with a good credit score and I can be approved, My grandmother said she would sign and she scores a 750 so after they checked her credit they approved the loan. It took me a couple of weeks to get them down to a decent price & payment but they finally did...anyways I told them to print out the contract & we would come in and sign....I got there about 30 mins earlier than my grandmother and they let me sign all my contract papers but before she could get there, my salesman come back out & said that toyota financing was not gonna do my loan because of my previous bankruptcy and me and my grandmother had a different address. Keep in mind that this dealership had checked mine and my grandmothers credit about 3 weeks before and they already knew all this info about us. I feel like I was fed a line of BullSh*T and they backed out because I had gotten them down about $3000 off the list and maybe someone at the last minute offered them more. This just doesn't make any sense at all to me.....does anyone have an answer to this????