I think the email option may be best as it establishes a support ticket with your email. Give as much information that you can to help track down your payment and reissue the license if it has gone to an incorrect email address.
You don’t have to have the subscription email as such, just the wrong one you entered and they can try and track that and any other information, name, etc.
From that page select the “How can I cancel my Avast subscription?” option.
You should also be able to open your existing Account right click on the AvastUI icon bottom right of windows > Registration that should end up taking you to the same area given in the above information. This is essentially the same Avast Account used to logon to the forums.