Person left - no-one attending to our queries

We have been renting vehicles through First Car Rental for a long time... In November we found out we were actually not dealing with First Car Rental but with one of their agencies. Service was terrible. And when we complained we were told go to another rental company. We just did that and from December 2015 we've been using Europcar...<br> However, First Car Rental has not paid our deposit back or finalised our last bill. The email address we were given does does not work.<br> Try to load a query on the First Car Rental site does not work either... even if all areas are completed a message pops up to say insufficient info... <br> This is really not great service... Sad to say...