Shocking service at Rentalcars.com. dont ever use these guys!!!

I booked a car 3 weeks in advance and paid in full when making the booking and rentalcars.com make it seem asif your booking is confirmed but it is now a day before I need the vehicle and they have still not confirmed with Europcar whether my booking has been finalised. I have tried contacting rentalcars.com without any luck as all their numbers are UK numbers or not working.