I keep going back when they are dramatically cheaper than the competition, but I've had so many problems (documented on FT) with Budget over the years it's amazing, and the mysteriously changed rate/terms was one of them.

I've found that "corporate" is just as crooked/lazy as the local branches in terms of getting responses to questionable practices. I suggest making a backup reservation and if the Budget agent refuses to honor the rate, tell them where to shove it.

Also, check that return receipt! The time I had an argument over my quoted rate, they initially relented when I picked up the car, but then changed it anyway and refused to budge when I returned it.