Catalysts can fail (I've replaced 3 on my Scorpio), but they normally make a rattling/tinkling sound beforehand whilst driving. Did any of that occur with your car?
Did Renault fit the cat?
The reason I'm asking these questions, is that I wonder if the cat may have failed due to something else not being 'right' (for example, the failure of a lamda/HEGO sensor - which measures what the exhaust gases are composed of, and adjusts the air/petrol mixture to suit).
It may be a case of the symptom receiving the treatment, instead of the cause.
I would suggest taking the car back to who carried out the work, explain the problem and get them to use a probe to analyse the exhaust gases - the engine may be running rich (which would explain why more fuel is being used).
How old is your car/how many miles?
Sorry for all the questions - no prizes for answering them all, but it will help to eliminate/put forward possible causes.