This sounds like a complete mess and poor service from the renault garage you have been dealing with. clio 2 ph2 when an impact as occured and the air bag
has determined that the accendent is serious enough to deploy the airbags, the airbag
has to be replaced. although it has run for five months. this should not have caused the car not to start out of the blue. When I was reading it I would of said it was either a decoder ring or a key fault have seen it alot in this model. So here we are, all i recon you needed to start the car was the key replaced and coded in to the interconnection unit. But this then knocks out any old key previously coded to the vehicle. The reason thay have fitted an airbag
is the impact fault would still be logged as a permenent red fault so they have just fitted it not thinking that somebody has to pay the bill at the end of all this. The garage should have explained each step and cost to you and made sure that you where awere of the full cost of the repair. What i would do is phone the dealership and and arrange an apointment with service manager then go see him in person and ask him to explain what has happened and what exactly the bill is for do not pay for anything untill you are happy. Remember that you are paying for an renault expert that is what they are there for so if he gives any vague answers or states not sure do not take this do not lose you cool cause doing this gives him the right to ask to you leave. If this does not solve anything the next step is customer services contact them detailing everything that has happened and what you have been told and that you have taken every step you can and leave it with them they will then contact the dealer and ask for there side of the story. Next if your still not happy, when you booked the car in you signed a job card this authorises them to check it for the non-starting when you give authority over the phone ie verbal this is not binding you can just pay for what you origanlly signed for. warning they have the right either to take parts back of or take you to court for the money. Also they can not refuse to give you your car back as it is your property the police will make sure that they return your car. My advice do not pay or sign untill you are happy they are suposed to help not screw you, a small garage wouldn't do.