Product Key was one time use but I returned my computer and need to reinstall on new computer

I purchased a Mac book and one time subscription to Microsoft Office and installed it on my Mac book. I retuned Mac book and before doing do I uninstalled office as requested. Once I purchased another new computer and tried to reinstall Office, it is saying this product key was already used since it was a one-time purchase.

I only installed it before returning the computer, so I don't feel it is fair to spend $200 on Office return a computer just for them to tell me, "Sorry you'll have to purchase another subscription."

How can I get this product key to work on my new computer?

Also, WHY is there no phone or chat help with Microsoft - I find it RIDICULOUS that you cannot speak to someone and every time you need help, they refer you to a bunch on online Q&As - that is NOT customer service. It is BS and should be ashamed. No live chat, no Microsoft stores, they just say good luck hope you figure it out online... COMPLETE BS.