If it was me, I'd tell them I was unhappy with what they have done, and tell them to make you an offer on a partial refund, or tell them to take the car back and give you a full refund.
If their offer is piss take I'd give them the keys. FSH is not 1 service on a car that's four years old.
Your out of Renault Warranty anyway (Unless its been extended?) so its not exactly like the lack of the service will affect any claims, with the exception of trying to claim something if your gearbox goes pop soon, but since there's no serviceable parts on the gearbox it shouldn't matter if you had your engine services or not.