how long are you waiting??
an absorption fridge can take at least an hour before you see any difference, check the feezer bit, the plate should feel cold after about an hour.
the 12V wont work unless it hooked up to your car, engine running at a decent revs, it will not work direct from your battery in the caravan.
if it lights and really doesnt work on gas, check that the van is almost perfectly level, it can have a big impact on efficiancy and if it works at all.
still not working, have the fridge removed, turn it upside down over night and then turn it back the right eway up, you may have to repeat this a couple of times, this re-mixes the ingerdients in the fridge if its been sat for a while.
if this doesnt work the fridge is U/S
they UK campsite, its a caravan/camping forum with plenty of knowledge on non-working fridges.
wingcoax, most dealers/service centres only check for the gas/electrical safety, not if stuff actually works, so this may or may not bring to light a fridge fault such as this. if it lights up on the front, they probably assume its working.