Hi Robert Ilu,
If you are sure that the product key is correct, you can try activating OS using the telephone activation method. To do this, follow these steps:
- Open the Command Prompt as an administrator.
- Type "slui 4" (without quotes) and press Enter.
- Select your country or region from the list and click Next.
- Call the telephone number provided and follow the instructions to activate OS.
For more information about phone activation, please refer to https://www.microsoft.com/en-sg/licensing/existing-customer/activation-centers?rtc=1#primaryR8
Regards,
Lei