I have a letter from the Mayor of the Commune in which I reside telling me that, as my European citizenship ended in January 2020 as the result of UK leaving the EU, I could neither seek to be appointed to office in the local elections, nor vote in them. My name has been struck off the electoral roll. Not an EU citizen, not entitled nor eligible to take part in the plebiscite. QED.
Plain as a pikestaff or the nose on your esteemed fizzog, old chap. Wake up and smell the coffee (I hate that inelegant injunction but it fits your obduracy like a glove).
More in sorrow than in anger… 
PS If you haven’t had the same letter yourself you are either not statutorily recognised as a resident in France or, if you are, you have not sought to have your name entered on the electoral roll; or possibly didn’t read or understand your advisory letter. Maybe you are not officially known to your Mairie?