Hello
The command you ran is for OEM license embedded in motherboard, since yours is retail, it will not return the key.
Since you have purchase proof, you can chat with Microsoft support and see if they would honor it with a replacement key. No one in the forum can grant such and it is entirely at support's discretion.
Although, before you reach out to support, Can you please type cmd in the search on the taskbar and hit enter to launch command prompt, then run the following command:
slmgr /dlv
Then share a screenshot please. Want to make sure it is indeed a retail key.