Fridges work by getting rid of heat, so put your hand over the upper external vent and see if you can feel any heat coming out. If not then you need to do some checks.
In most caravans the fridge supply is through a 13A plug somewhere adjacent to the fridge. Pull the plug out and see if something else plugged in there works. If it does check the fridge plug fuse - if it is 3A (blown or not) change it to 2A or 5A as 3A fuses are notorious for mechanical failure (as distinct from blowing.)
If the test item does not work then you need to go back to the power box and make sure that is also working. Note that the fridge is usually connected to the 6A breaker along with the caravan charger/power supply, therefore is the charger/power supply working? One assumes that all other mains kit (e.g. 13A sockets) is working thus proving mains is reaching the 'van?
Your 'van, like most others, will probably use the cheap and nasty Chinese breakers (MCBs) and RCD, the latter of which is also known to fail inexplicably, but that would remove all mains. Nonetheless if it has failed get a Schneider 40A/30mA RCD from Toolstation - cost a bit over £20 - and fit it or get someone who knows what they are doing to fit it for you.