Failure to assist

On visiting the UK, we hired a car online through [URL Removed] and used a company called Interrent. There were no problems with the collection or the use of the car. However, on returning the car, we ran into problems. Interrent is not situated at the airport but is a few miles away from Heathrow. We had been given a map when collecting the car, but despite this, we were unable to find the Interrent office again. We drive up and down the M4 and A4 with no luck, and time was running out for us to check in for our return flight. As a last resort, we decided to head towards our terminal at Heathrow and call Interrent and ask them to assist us. Bear in mind we had no cellphone coverage or a SatNav. I called Interrent from the airport and asked if they could come and collect the car. They refused. I begged them to help us and was in tears as I explained we'd tried to find them but couldn't and now we needed to check-in. I was told that if I didn't return the car, then the police would be contacted. Since we received no help, we opted to drive to another car hire company to see if they could direct us to Interrent - and we eventually found the location.