ford mondeo zetec 1.8 Tdci eating diesal

Hi

I bought 07 ford mondeo zetec 1.8 tdci only 2 weeks ago through finance in a garage, and its absolutely eating diesal I cant keep it into it , its costing me a fortune, my last car was a 2 litre diesal opel vectra and 35 euro a week would get me too and from work (which was 44 miles a day back and forth and 220 miles a week) and maybe on few little short trips so I was expecting this one to be in around the same,I rang the garage as its under warranty for 9 months and they said there is no way it can be going through that much diesal and to bring it into them on Friday, since last friday 40 euros in diesal has disappeared and the diesal light is back on and its only Tuesday and I have only been on a few small trips as I am off work now on Mat leave, if this continues can I hand the car back to the garage or what is my rights if I have already entered a finance agreement am I stuck with it? or does anyone know how this car is going through so much diesal, I know a few people with the same car and they dont have this problem thats why I bought it in the first place.

I've a 2.2 tdci mondeo and it does about 570 miles to the tank and averages about 49mpg.

I am going back to garage tomorrow, I had it looked at by a mechanic I know and he said it prob wasnt serviced before it left the garage because the 'flywheel' is going in it, so hopefully with a good service it will make it easier on diesal