I have similar issue with a van I hired in the Orpington branch. I rented it for only a couple of days, when the delivery guys dropped off the van they did not even wait to check to check the vehicle in detail and they left it in front of some other cars obstruction the way, by the time I when into the cabin to check the mileage and fuel, they were already gone.
The fuel thank turned up to be not full, I called the branch several times and left voicemails explaining the situation but no one bothered to answer, they seen to be having a barbecue or something because this was the case throughout the whole day.
On the day of collection I called again and after several calls, I finally got through Carol who I spoke to an informed her about the fuel thank issue, she said it is not a problem, I put some notes in your file.
Well, I guess you know what is coming......Yep they charged me double for a full thank when I returned with more fuel than when they delivered the van.
I have sent them evidence and so far no refund has been made, they say 10 days but this has been the case since the van was returned on the 22nd July 2013.