Cannot Activate Windows 10

[Capnralls]

I purchased a refurbished Lenovo desktop. On the back was a sticker with product key. The part that was silver to rub off to show full product key. I rubbed too hard and wiped out part of product key. I contacted seller they couldn't help me, said I would have to purchase new license from Microsoft. The price for new license was $139. Is there a cheaper way for me to get a product key so that I can activate windows? I have been using Windows 10 but I keep getting messages to activate windows. Please advise.

 

[rgd1101]

either buy it or run it unactivate.