Hi Elaine Cheung NAVIS,
Welcome to Microsoft Community.
Normally, the red light flashing indicates that the battery installed on the keyboard is low. Considering that you've got a new battery and the red light is still flashing, you can't rule out a keyboard hardware problem. For services related to hardware issues, you can visit Microsoft's customer support page
follow the screenshot in the screenshot below to go to the page for contacting customer service (you can choose online service or phone service).
- Type "Microsoft Keyboard" and click "Contact Support" at the bottom of the page.
- Enter "Other Products" for "Microsoft Accessories"
- You can choose online support or telephone service to contact Microsoft after sales support staff.
Hope it helps! If any update, welcome to share with us.
Best Regards,
Manson | Microsoft Community Support Specialist