Your official homepage says something different. Mobile devices are included.
Source: AVG Internet Security Software | Online Protection | Free Trial
So, Internet Security includes Android too. So, why I can't activate the licence? 
We'd request you to submit this query to our dedicated Android product support team for a quick resolution.
Please click the link below on how to contact them from within AVG app:
https://t.co/UfBrCxE96i
Thank you.
Hello!
I have bought an activation code on a serious key-seller-page on the internet and activated the AVG Internet Security license on my PC and my Notebook.
On my mobile Android device it doesn't work. The same activation key…
Can you please help? Is the code for AVG Internet Security (3 devices) not for Android?
Hello Kevin.
Thank you for contacting us.
Please note that your 3 devices license can be installed on 3 Windows devices.
It is not compatible with Android devices.
Hello Kevin.
Thank you for contacting us.
Please note that your 3 devices license can be installed on 3 Windows devices.
It is not compatible with Android devices.
Your official homepage says something different. Mobile devices are included.
Source: AVG Internet Security Software | Online Protection | Free Trial
So, Internet Security includes Android too. So, why I can't activate the licence?