First, just like air carriers & hotels, even a confirmed reservation does not equate to availability. Car rental places sometimes either overbook or people do not return on time or the vehicles are returned damaged or otherwise in poor enough condition that they can't be sent back out. So, consider what you would have done had there been no cars available at any rate.

Second, while people sometimes bash US customer service in general, the typical response here, presuming availability, would have been to upgrade to the first available car class and then invoice at the lower rate. In many parts of the world, this is simply not done. Knowing that the franchisee could turn you away, the decision is not to upgrade as a customer service gesture.

This leaves you with few to no options. Try the short & sweet complaint to corporate. Your posts are 3-4 times longer than they need to be. Stick to the relevant facts which are simply that you had a confirmed reservation for Car X at Rate Y and it was not available. The only resolution offered was a Car Z at Rate Y+70. You want a refund of the 70 x # of days.

Repeating that you kept calling back doesn't do anything. Of course the guy hung up on you, you had his answer !