Ok let me first point out I've got all 3rd Party addons disabled.

Now if you take a subscribing member and and login as him and them go to the subscription page there is no cancel button to cancel a current subscription or the ability to up or down grade a subscription. I've also seen where the buttons are not present to new member to subscribe. That I found was a 3rd party add on that caused that and disabled all my 3rd party stuff. Still in all there is no buttons to cancel a subscription. Now doing some testing current subscribers do not have any cancel button. Any non-subscribing member does have a subscribe button. Existing subscribing members do not have an option to up or down grade. 

Even went as far as using the support link and disabling all addons. Making sure when I log in to a members profile and used the IPS default theme and no luck buttons are missing. No cancel button or up or down grade buttons are missing.

I have created a ticket on this so we can take a closer look for you

Thank you... 😁