Hi when you press the button on the key (open or close) does the red light come on, on the key . If it does not and the battery is known to be good . It would suggest that the battery holder terminalhas become detached from the board . This seems to be a fairly common problem . Assuming the light does not come on and the battery is good take the remote apart and press the battery down on to the board and try it then, if the connection is broken you should be able to get the light to come on . If it does and you can resolder the joint you should be able to do a repair . Another semi repair is to pack the battery with cardboard so it presses everything together to keep contact .
I have done both these repairs in the past .
Of course the other problem could be that the remote is not the one coded to the car, and these need to be recoded using tech11 for which yoiu will need your car pass . Which is why I have not got around to geting my spare remote coded yet

I really must get around to do this

I hope this helps and at least makes some sense