First of all, thanks for your sharing and the amount of patience you have.
I have no intention, though, to waste a single minute more of my life dealing with a totally unprofessional support. It does not exist, that it.
I hope any in this forum and everywhere will be able to solve this issue, one way or the other. I did what some Microsoft 'tech support' have done, using a third party software to unlock the stuck license, which I payed good money as you did, and I have all invoices microsoft should be asking for.
For now everything is working properly on my machine, even though the issue wasn't fixed by the official support, I'm ok with that. Hopefully microsoft will wake up from the lethargic deep coma and finally acknowledge this is an issue affecting many of their (paying, once more) users. I put the emphasis on the 'paying' point, just to balance the times troubleshooter suggested me to fix the issue buying a license, just assuming I had a pirated copy of my OS.
I don't know if I will be able to use again this license since I tend to change pc once every decade or so, but to be honest I don't want to think about it since now
Have a nice one everybody, and good luck