Hi H,
Thank you for reaching out on Microsoft community, regarding on your issue "Unlocking Microsoft Surface after Airline Found and Returned"
just to confirm this is your personal device and not managed by your company and also you have a good internet connection? if that's so
you can try to reset your surface;
In this case, you may need to reset the device using recovery options:
Hold Volume Down + Power to enter recovery
Choose Reset this PC (you can keep files or remove everything)
then try to reset it again on account.microsoft.com/devices
Please let me know if it works. I await your response.
Warm regards,
JayMark.D | Microsoft Community Support Specialist