Every time I try to set up voicemail it says I don't have it activated on my account does anyone know how to activate it?
Looks like you can do it under the Your Products > Landline>Manage section of the web site. Then click on "Show more landline features" at the bottom of the page. This link may or may not work for you.
https://my.bt.com/s/apps/appsmybt/#/landline