fridge/freezer hotpoint ffp187b?

My fridge/freezer is coming up to 7yrs old and we have recently noticed food has not been freezing correctly. I have removed the drawers from freezer to discover large block of ice at the bottom and the vents behind the third drawer are frosted. There is a plastic clip behind the top drawer which I removed and can see a large snowball of ice surrounding wiring.
The freezer section (fan) has now become very noisy making a vibrating noise which I assume is the fan trying to work and the only way to stop it is to open the fridge door.