U-Haul at Alameda Ave

I rented a truck from the U-Haul at 2645 W Alameda Ave; Denver, CO 80219 The next day I received the receipt for the rental the next day, I drove the truck 13 miles and was told by an individual answering the phone that the trucks get about 15 miles to the gallon. Two block before returning the truck I stopped and got gas, I actually added more gas than what was required and I have the bill. The receipt showed that I was charged $30 for the fill-up service and $7.50 for gas which should have never been charged. By their own employees admission 1 gallon of gas would have been sufficient for the the 13 miles I drove and I put in 2 for good measure. I was also charged for a mirror that I used driving the truck back. I have not spoken to anyone at the location about this to determine what they are talking about. I have tried to contact this U-haul location Sat the 19th, 2x's Mon the 21, Tues the 22nd, and 2x's Wed the 23rd. I have spoken to employees at the physical location, the call center, and regional office as well, every time I have called they said the manager will call me back. Still no call, not even a try. I work during the day and I could forgive if he had even tried but they don't care.