1yr old fridge not working

To anyone that can help!
I bought a nearly new hotpoint fridge second hand. It was under a year old and barely used. I transported it on its back for about a mile, then left it to stand for 48hrs before plugging it in.

It ran totally fine for about 4 months, then I noticed the compressor was running all the time and some ice had built up at the back. I defrosted it and carefully removed the ice then switched it back on.

Now the compressor runs all the time, everything appears normal, but the fridge doesn’t cool. If anything, it’s warmer inside. I can’t seem to find the problem. It’s outside its warranty, but pretty much perfect condition.

Any ideas what it could be?

Many thanks.