It's also normal. Costs fluctuate, things change. My first quote from reliable was $2400 for the same trip, two days later it was $1850, the next it was $2175 - the actual cost on the day the car is accepted is the only 'valid' cost and most carrier contracts state the same. I went with affordable two days later, who's quote did not change, but their schedule sure did. It's pretty normal based on my experiences with contract shippers.
I'd review your contract to see if that was spelled out before hand. If not, your frustration is warranted. If it was, you might be getting stressed over 'nothing'.
