I have found my order in My Subscriptions Portal and clicked Manage Subscription; however there is no link that is active and lets me turn autorenewal OFF. The only active link is to renew now.
I have sent tickets but I do not know if they transmitted successfully because when I clicked the SUBMIT button, I was returned to the SUPPORT HOME screen with no acknowledgement. 
Maybe this will help.
Disabling Automatic Renewal service for Avast orders distributed by Nexway
https://www.avast.com/en-us/faq.php?article=AVKB136#artTitle
Disabling Automatic Renewal service for Avast orders distributed by Digital River
https://www.avast.com/en-us/faq.php?article=AVKB126#artTitle
You can also look at/change the auto-renewal yourself here https://www.avast.com/find-order
I am also having the same problem. I had tried both the methods you have given before I saw this thread, but to no avail. I have successfully cancelled auto-renewal twice recently (on two other devices), but no luck this time.
When I try to cancel on my Subscription Details page there is no ‘Automatic Renewals - On/Off’ option like there should be.
When I try to cancel on my Your Licences page there is no ‘Cancel Auto-renewal’ button.
My Order ID is 32600433862.
Maybe somebody can help, please…
Thanks
Leon
Hi, leondannydiamond.
Please, contact support: https://support.avast.com/en-us/contact