It should be possible to get an emergency immobiliser unlock code but it will likely be a fiddle to put it in every time you want to start the car.
Have Renault run diagnostics on the car to come to this conclusion?
If not, a new antenna ring for the immobiliser may fix it, reckon it will be a hefty amount cheaper than a new
box. The antenna ring recognises the transponder in your key, if it has loose wiring or is damaged it could cause this problem.
I have read through Renault docs and they seem very quick to throw replacement parts at things instead of actually finding the fault, they leave a lot of grey areas, nothing solid at all. NOT impressed.
Their attitude is, test a bit, not working? if it might look that way, replace everything, their ethos is replace replace replace.....replace again...etc. Still no good? best off scrapping it then, they don't care about your custom/problems at all, they grab and run.