if the fuse is OK, take a look at the actual grid on the rear window.
Sometimes, from wiping the glass, or objects rubbing against the glass, the line on the window, (those lines are the actual electrical resistors that warm the glass), will get a break somewhere.
It doesn't take much, because thos lines are just like a wire.
One break or missing stop, and the circuit is broken. Doesbn't work. Kaput.
If the break can be seen, you can get a bottle of resistive repair from the auto store. Just brush (carefully) the liquid on the missing spot, to re-complete the circuit. Don't get messy, or think that more is good. - It's not.
You just want to re-connect the line, (only) where the break or gap is. It usually takes only 1 tiny dot to do the job.
Good luck.