Avis Rent-A-Car Over charging Katy Texas

I rented cars from AVIS once in December and three times in January while my car was in the shop.  The agreed rate between AVIS and the auto shop was $30/day.  I had the car for 1 day each time.  I got charged $30 for the December rental.  The January rentals came to $60, $565, and $135.  They claimed I had the car a week and returned it 250 miles away.  I was supposedly returning a car 250 miles away while I was at work.  And they charged me $30 for tolls in that city.  I called and explained this didn’t happen.  They told me they would refund the money within 48 hours.  They did not.  I called at least 4 times and each time I was told they would refund the money within 48 hours.  They finally refunded $290 of the $700 in overcharges.  They have been unable to produce paperwork showing where I was the one renting the car for those dates.  The auto shop has told me they have received several similar complaints, (AVIS stealing money) and are changing rental agencies.