IME the most common cause for a freezer that warms up is that it is a frost-free freezer and the air ducts at the back are clogged with ice.
If so, the fix is fairly simple and certainly worth trying.
Take out all the food, and cook and eat it (or store in your spare freezer, or pile it in cardboard boxes, and wrap the pile in duvets.)
Unplug the freezer from the electricity supply. Preferably pull it away from the wall (it is lighter now you have taken all the food out) so you can see the drainage dish.
Leave the door open for at least 24 hours.
Since the ice blockage is in ducts inside the lining, you can't see it, so it is not enough to melt the visible ice.
Observe that water drips out of the ducts inside the freezer, and also from the drainage pipe behind the appliance, which runs into a plastic dish on top of the compressor/motor. Keep sponging this dish out (it will be very dirty, and might overflow). Leave the appliance door open, and turned off, until water has stopped dripping front and back. If you stop early your efforts are wasted.
When it has stopped dripping, wipe it dry with clean kitchen roll, verify that it stays dry, close the door and turn it on.
If it happens again in less than a year, there may be a cause such as the door left open too much; the door seal not tight; or the duct defrost heaters not working. This can be repaired at substantial cost.
If this does not cure the problem for even a week, it might have lodt gas or have some other problem, and needs either professional repair, or tipping into the skip, because cost of repair is not worthwhile.