Hello my name is***** and I would be happy to clear some things up for you.
First, we are not Microsoft. I am not sure if you were under this impression.
Windows 10 activation gets a little confusing. I myself experienced some confusion with this.
Here is what you need to know. You MUST do an UPGRADE ONLY to Windows 10 from 8.1 first to get your computer activated and to obtain the free Windows 10 license. Once you have upgraded you can then do a CLEAN install and your PC will automatically activate. You do not, and should not have needed to purchase any license. If you did I would fight with wherever you purchased that for a refund.
The main thing you need to do is choose the option to SKIP entering the product key. It is not necessary.
I hope this helps. You really do not have to buy anything. That is the whole point. Once again, I would fight that.