Can you post the model number please.
all i can see is that it is an A class is that any help
Ok is it about 5 foot tall?
If you open the door look at the top at the front do you see a vent there? If so look in there or shine a tourch in there and do you see a build up of ice in there?
yes it is about 5 ft tall i have looked into the vents but to be fair i could not really see any ice there
Ok what you may find here is its either the evaporator is blocked with to much ice at the back and has stopped the airflow or the compressor is the problem.
What you can try first is empty the freezer and turn it off for 24 hours and leave the freezer door open. This will allow the ice in there to melt and clear the air flow. Then turn it back on and see how it goes from there.
If it works which fingers crossed it will keep an eye on it and see how it goes as if it does it again then you have a defrost issue in there which could be either the defrost heater, thermal cut out or the control board at the back.
But if after the defrost its still the same then theres a system fault which usually on these is down to a compressor. For this you will need to get a fridge engineer as they will need to put there gauges on the pipe work at the back and check the running pressure of the compressor. But if it is the compressor then this isn't cheap fix. You are looking at roughly the £200 mark so maybe not worth fixing.
But try the defrost first and see how it goes as this does happen a lot on frost free appliances no matter what make you have.
If you need anymore info just get back to me.