Here in the States we use Easy-Off Oven Cleaner
to remove old hand-painted lettering.
I am sure you have a similar product "over there".
It is a caustic, stinky aerosol oven cleaner.
It can only be done indoors, working a small area
at a time. Spray it carefully on the lettering, or
spray some in an old ceramic dish & dab it on
with a cheap paintbrush. Then carefully scrape the
whole mess off with a L'il Chisler or a plastic razor blade.
You must test it in an inconspicuous place first
(not yer armpit) to see if it will damage your underlying
paint. Never do this in the bright sunshine.
I think if it were me that I would maybe just paint
a patch over the whole thing, or stick on a vinyl
patch. Sounds like a pain in the butt.