VPN Activation Code

Hi,
I purchased a one computer license for VPN for one year. I got a new computer and sold my old one. I would like to activate this for my new comptuer and deactivate it from my old computer. I am not seeing how to do this. I can get a license file that errors on load and my options on the VPN program is to activate it with my account that seems to fail and the license file wont load. It seem to want an activation code that I did not receive during purchase. I am unsure what to do. Help would be greatly appreciated.

Thanks.

https://www.avast.com/faq.php?article=AVKB24#artTitle (Orders and Renewals)