I have tried to unsubscribe via customer support, problem is the e-mail address used when I purchased is not longer valid.
I can not come around this problem because support ask me to verify my no longer valid e-mail address trying to send their
mail to it 
Please help!
You could first try changing the associated email address, I don’t know if this would also require validation.
Sales change order details wrong email address given, etc. - Submit a support ticket https://support.avast.com/en-ww/contact/sales in your case select the Billing, payment, or license issues option - and then the I have a different billing or license issue and click Next and select your preferred communication method.
Thank you very much, your answer helped me solve the problem 
You’re welcome, thanks for taking the time to let us know it is resolved.