Hi DJChristie1,
Thank you for reaching out to Microsoft Community.
Try to press and hold the pairing button at the bottom of the mouse for 3-7 secondsand see if the LED flashes. If it does, please go to Windows Settings > Devices and try to pair the mouse again.
If still the LED does not flash or unresponsive, this is likely a hardware issue already as you have changed batteries already. I suggest that you contact support through our Global Customer Service phone numbers to check for replacement options available for your Surface Mobile Mouse.
If this answer your question, we highly encourage you to inform our Community by clicking on Yes or marking my post as an answer. This will help other members who may have the same issue as you. Otherwise, don't hesitate to update us so we can further assist you.
Kind Regards,
Marrion Y.