If you've put a new battery in you need to reinitialise the keyfob. It tells you how to do it in the owner's manual but here is for convenience. Give that a go first.
REMOTE CONTROL PROBLEM
Following disconnection of the vehicle battery, replacement of the remote control battery or in the event of a remote control malfunction, you can no longer unlock, lock or locate your vehicle.
First of all, use the key in the lock to unlock or lock your vehicle.
Then, reinitialise the remote control.
Switch off the ignition.
Turn the key to position 2 (Ignition on) .
Press the closed padlock immediately for a few seconds.
Switch off the ignition and remove the key from the ignition switch.
The remote control is fully operational again