Microsoft often doesn’t repair your exact unit. They send a replacement device with a new serial number
Your old device is removed from your account automatically
Result: It disappears from devices.microsoft.com
Visit: https://support.microsoft.com/devices
Then:
Choose Surface
Select Check repair status / Contact support
You don’t have the serial number, so self-tracking won’t work well
Support can locate your device using UPS tracking + your email
If a replacement device was issued, then a new serial number will be provided.