Hi C
My name is Andre Da Costa; an Independent Consultant, Windows Insider MVP and Windows & Devices for IT MVP. I'm here to help you with your problem.
If you decide to cut your losses, you can always purchase a genuine Windows 10 Pro license directly from the Microsoft Store. You will receive the product key by email:
Buy Windows 10 Pro - Microsoft Store
https://www.microsoft.com/en-us/p/windows-10-pr...
You can the update the product key values in Windows 10 Pro and it should automatically activate over the Internet.
Click Start > Settings > Update & security > Activation > Change the product key then enter the new product key then click Next to Activate
You should still try reaching out to New Egg though since they are reputable site and indicate to them the product key is no in the package. Sometimes theft happens and the product key usually stolen.