You sold a property in France in 2017 or 2018? You could be entitled to claim a french tax refund (17,2%). 100% GUARANTEE!
You could claim the refund of CSG CRDS and other social security contributions if you have been taxed in France, but are affiliated to a social security system of another EU member state or Switzerland.
More precisely, it is the case for the cross-borders commuters living in France but working in another EU member state or Switzerland.
It is similar for non residents living outside France, working in another state of EU or Switzerland, but having earned income in France (rent or capital gains) subject to social levies.