Hi hansw, welcome to the forum

Is the email address from your Avast! Account the same as the email address you purchased your licenses with ?
If not, go to
https://my.avast.com log in and choose :
Your email - Manage Emails - Add New Email - Fill in the email address you purchased the licenses with - Click the blue button.
An email will send to that email address. Confirm it by clicking the link in the email.
Go back to Manage Emails as descriped above, and click for the new email address on : Primary set.
Now you should be able to use your licenses from your account.
That said, when you bought your licence(s) you should also have had an email with a license file.
You can have resend that to you as well
https://www.avast.com/en-eu/resend-license-paid.phpGreetz, Red.