Reprogramming Remote Key Function

[France]

I know this topic has been somewhat covered, but I still haven't managed to sort out the problem. We had to have the ignition assembly and what in French is called the "nieman", which I believe contains codes for the immobiliser, replaced. (Please excuse my lack of technical knowledge!).

Since getting the car back, the key will not work remotely on the central locking. The central locking itself works fine and I can unlock and lock the car by using the key in the driver's door. I have changed the batteries and I have tried one of the reprogramming methods posted here, but it still doesn't work. I only have one remote key.

The garage says it has nothing to do with the parts that they replaced and that the fault lies with the key (which admittedly has seen better days). It just seems like too much of a coincidence. Can anyone shed some light on this for me?