National Car Rental review: Overcharged, charged 3200.00 more than rental contract!

We were traveling to Dayton Ohio and hit a deer, which totaled our car. We got no answer from the local enterprise office, tho they were listed as open another 2 hours. Luckily a wrecker drove by and took us and our car to a shop in the nearest town, we were able to get a relative to drive 85 miles to pick us up with our belongings and take us to the Lexington airport to rent a car. After the paperwork was all done, the clerk from National Car Rental told us how to return the car there, we had told her we were returning the car to Huntsville, AL. She told us that would be no problem, although she had already put it in the computer for return to Lexington, KY. I then asked her to please delete the rental agreement and re-enter with Huntsville Al as return site, she refused to change the contract saying it would be no problem, the contract was for 1000.95 dollars with a 300.00 deposit. We took the car and completed our trip, when my wife turned the car in at Huntsville airport they billed our credit card 4500.00. We have made numerous calls to National, and wrote the BBB, one agent in Lexington said that the clerk should have voided the original contract and rewritten. We had received only one return call from National, while we were driving to Durham NC for my brothers' funeral, my wife was driving, and I was asleep in the car, she was driving and could not answer the phone. We have made several attempts to contact the person back but have had no luck. We are not going to just let this go, they owe us, 3200.00 Thank You