I can't help with the problem but hopefully one of our more technically minded members will be along with some advice.
I can sympathise with you, I had similar problems with my last car (E Class Merc). It first let me down when it was just 3 months old and I could never trust it. When you've got young kids and you don't know whether your car will start it's a pain in the
Sounds to me like it's time to insist that the garage find the problem rather than just getting it going again. It could be worth getting Renault Customer Service
† involved - not necessarilly to have a go at the dealer but to fix the problem.
Good luck with it.