The remote key fob of my Fabia Vrs MK1 2006 has stopped working it won't remotely unlock or lock the car, it will start the car no problem.

I used to have a prompt sheet to re-sync the key (when this happened before some years ago) but have mislead it and all the different solutions I've found on the Internet so far have not worked.

The other key works as it should.

Have you tried replacing the battery?

Yes, sorry I should have put that I replaced the battery with a new one.

Does the indicator led on the remote fob light when a button is pressed?

Yes it does, on both the original battery and the new one.