Halfords may have fitted a DAB splitter, a powered component, behind the set and it may have failed.
Windscreen aerials are next to useless at the best of times and as BHG notes, Renault screens are problematic. There is most likely a black area around the mounting for the mirror where things like gate openers and the like can be fitted.
What you really need is an aftermarket DAB/FM aerial, fitted by a specialist car audio installer, not Halfords.
They're expensive but worth it.