How do I stop an old subscription from being renewed?

I’ve just received an email stating my Avast annual renewal is due; which at first I thought was odd as I didn’t start it until June 14. Then I realised it was for my netbook which was damaged at the start of the year & is usable. Do I just instruct my bank to block the payment going out or do I need to inform Avast? I can’t seem to find away of contacting them that isn’t technical support?
Appreciate any help

Please use the search option before posting as this has been explained many times already.
https://forum.avast.com/index.php?topic=156540.msg1133461#msg1133461