Hello Sam,
If this is a custom-built computer, I don't think you purchased the license directly from Microsoft, right?
I think what you have is an OEM-NSLP license. Did you peel off the sticker and apply it on the computer somewhere? Typically builders should do that if they are 100% compliant because that's required by licensing terms.
Microsoft cannot replace these keys because they are not retail licenses purchased directly from Microsoft.