Hi,
Thank you for writing to Microsoft Community Forums.
We understand the inconvenience caused to you with the upgrading procedure to Windows 10 Pro. There are authentic third party vendor who sell legitimate copy of Windows 10 and there are also some third party vendors who sell pirated/non-legitimate copy of Windows 10. As you have already checked the license copy with Microsoft support team, then in that case we would like to know few things.
- Are you getting any error code/message while upgrading to Windows 10 Pro?
- Are you able to fix the issue when you spoke to Microsoft?
If you still have the issue, then we would like you to perform these steps and let us know the status.
Using default key
- Press Windows + I key to open Settings.
- Click on Update & Security and select Activation from the left pane.
- Click on Change Product key and enter this default key: VK7JG-NPHTM-C97JM-9MPGT-3V66T
- Follow the onscreen steps.
- Once the PC upgrades to Windows 10 Pro, then again perform step 1, 2 & 3
- Now enter the new product key that you have purchased.
Also refer this article for additional information:
Get help with Windows activation errors
Regards,
Aditya Roy
Microsoft Community – Moderator