Billed for 2 days, car rented for only 1 day

I rented the car on Friday 26 February at 7:10am, and returned the car on Saturday 27 February 7am however the AVIS/BUDGET offices were not opened by then, therefore I took the car keys with me because I wanted to dispute the state in which I found the car in, on Friday, unfortunately the offices at Hatfield don't have the cameras to show that the car was returned at 7am, the AVIS/BUDGET offices open at 9am on Saturday - the car is registered to have been returned at 9:20am on Saturday, however my challenge is that I was charged rental for 2 days, even though I had the car in my possession for 24hrs and handed the car keys at the office 20 minutes after they opened doors for business on Saturday - I feel that I was ****** because had the branch been opened for business at 7am, none of this would have happened - now I was charged an extra day's for only handing the car keys in 20 minutes later.