I have now downloaded the special offers for Premium two year and for Clean-Up one year. In both cases the time still outstanding on the original subscription has not been added.
In both cases I went to "Other available subscriptions" and activated "Switch to this subscription" and received the "Done" confirmation.
The previous expiry date for Premium was November 2022. It is now shown as June 2024. It should be November 2024.
The previous expiry date for Clean-Up was May 2023. It is now shown as June 2023. It should be May 2024.
What can I do about this? I am in Australia and my phone contract does not allow me to phone the Avast help number in USA.