Upgrade Windows 7->10, bought Parallels 13 an new iMac, Now I can't activate Windows

I'm using Windows 10 (version 1709, build 16299.402) on a Mac.
I upgraded Windows 10 from Windows 7.

After buying a new Mac and purchasing Parallels 13 Home Edition, I installed Windows 10 (under Parallels 13) on the new Mac.

I can not activate Windows 10 (The product key of Windows 7 is available to me), the error code is 0x803FA.

The Windows support tells me that only Parallels is competent.
Who can help me?

 

Hello rm.cmweb.de, Kindly remove the current Windows installation by following this link . Please download the Windows 10 home edition from this link < http://www.microsoft.com/en-us/software-download/windows10 > and install it ( refer https://bit.ly/2G4tRVc for asssitance ) please enter the Windows 7 activation key when it prompts for the product key.

 

Hello AJ, thanks for your response.
First off all i will read all documents.... I will give answer as soon as possible.

 

Sure, Please feel free to reach us any time for any queries regarding Parallels and we are here to help you 24/7.

 

Hello AJ,
I follow your description. Until yet i didnt the notice again!! Thank you very much.

But:
I created the user accounts (on for a admin, two for normal users).
And then suddenly I see one of my old user accounts.
How is that possible?

(When i started Parallels and Windows 10 I see the old account! I cant type in the old password. When I change the (old) name in the box into the new admin account name I reached the new admin account...)