Remote control battery message?

Hello I have a 2007 Astra covertable but remote control not working. Had battery replaced because message 'Remote control Battery' showed so took key to dealership. They changed the battery in the fob. Still not working and the message is still showing.
I have tried resyncing by inserting key into ignition and turning it to show lights but not switch on ignition, then pressing the unlock button. Did not work so I tried again and pressed the lock button still not working. Any ideas?