as far as i can see from other people on the internet this mostly happens when they go to the wrong region(such as going to US instead of EU), have you made sure that the battle.net page is the one for your region?
This can also happen if you have multiple starcraft 2 accounts on same email, then you need to migrate one or contact blizzard support.
If non of this things are your problem you can try this
When I login, I receive the message, "NO STARCRAFT II LICENSE FOUND", and I cannot post.
Simply try logging in and logging back
out. If that does not work, you'll need to flush your account cache.
To do this, change something on your account: your password, e-mail,
address, etc. Changing anything will reset your account cache.