There is no individual fuse for the licence plate lights, they are both fed directly from the footwell module (same as a few other items are), so you'd notice a lot more things not working if this was the issue.
There are, also, no replaceable bulbs for these either as they are fixed LED units.
I've tried the aftermarket replacements before and found them to be crap, so for not much more money you can buy genuine originals.
Personally I'd take one out and check you're getting voltage to it first though