rental car reimbursement

2005 or 2006 I took my Ford sports trac to Kuaffman to have my tires rotated. The serviceman did not replace the lugs on 1 wheel. One block away my truck fell to the ground. The back panel of the truck bed had to be replaced, a tire and rim was replaced w/o out problems. A week later my truck stated cutting off. I was told by a repair person outside the Kauffman company it was my alternator. I replaced that. It still cut off.
To come to find out Ford engineered the gas line to cut off automatically
upon impact. I took it back to Kauffman. They repaired it. Kauffman told me to rent a car for the time they had my car for repair. When
I tried to get reimbursemnt for about $300 car rental they would not repay me unlessI signed a paper saying I would not hold them responsible for anything else wrong with my truck. I would not because my truck did not ride the same and I did not know if anything else was wrong. I just said forget and i'd swallow the loss, but everytiem i think of it I get angry

Did they have the right to withhold my reimbursement. They did not say
I had to agree with that when I was told to rent a car. Is it too late to do
anything now. - Is this your question? Add additional information