The only way to contact Microsoft Support directly is to use the Get Help app in windows or their webpage.
Search the phrase billing then select Contact Support at the bottom of the window. There will be a couple more filters to select then you should see chat with an agent in your browser.
You will need to prove the history of the licence you are using so having that detail will help.
If it was part of the free upgrade from Windows 7/8 to Windows 10 it is no longer valid for Windows 11. You can only use an original Windows 10 licence to activate windows 11. (even though it was activated prior to the bios update)
Did you buy the licence separate from the previous PC or was it provided by the system manufacture/builder?