If Im wrong , np but.
I think what you mean is the fuel cover wont shut properly.
It will lock yes? the second pic, the upper part with the bit with the hole in it is where the locking solenoid pin goes into?
I cant see if the plastic bit that seem to be broken in pic 1 is a continous moulding with the whole fuel filler moulding or not.Hopefully it isnt.
Call up your renault dealer spare parts dept guy.
They will have schematics of the smallest areas,that they can call up on screen, and will probably be able to give you a better answer even over the phone.
If not call in to them n mr spare parts guy will probably swing the screen around so you can see the parts.
Hopefully that little locking ring that seems to be broken is a push/pull fit.
If it is all one piece
and its too expenxive you could probably bodge up something with kitchen cabinet catches/similar,even magnetic ones with a lil double sided tape, from your local DiY hardware store.
My last car the central locking solenoid on the fuel cap failed after like 5 years, I never replaced it as the flap would still snap closed.
Could you clarify if its the flap wont lock, or wont stay closed ?