Freezer not freezing properly

Hi everyone.

As title suggests, Samsung fridge freezer model no rsh5sbbp.

I noticed recently it's not working properly, ie lollies melting and bread softening. Seems to be even throughout the freezer.

Emptied and switched it off last night. Cleaned out inside and defrosted the pipes, and cleaned out the coils at the rear.

Checked on it this morning and there's no improvement.

The temperature on the front says -18⁰ but it clearly isn't. I did notice after turning it back on the temperature dropped from 8, 7, 6 etc but the last I noticed it was 2⁰ and then suddenly -18 in the space of 30-45 minutes.

It's also been a bit louder than normal recently, particularly the last couple of days. Humming noise.

Before I call someone out, what parts are the most likely culprits that I could try to replace myself?

Should be noted it's about 13-14 years old 😳

Fridge side seems to be working fine.

Edit the compressor fan is running. The humming noise seems to be coming from the compressor. Turning it off and on (again) at the plug I can hear a clicking. Before I turned it off the temperature on the front said -18. Now I've turned it back on, the humming noise has stopped and it says -5. It was turned off for about 20 seconds.

Evaporator fan is running.

There's a red led light on the control panel on the top but I don't know if that's supposed to be there.

Thank you in advance.