Pause and cancel are only offered on the customer's current subscription (the one holding their latest scheduled date); on an older one you only see Go to Current Subscription. If the subscription is already cancelled you see Uncancel Subscription instead, and trying to pause it returns "This subscription is Cancelled." If pause/cancel reasons are enabled and the reason you picked no longer exists you get "Unable to pause the subscription because the reason isn't available, please try again!" (or the matching cancel-reason message) – check Cancel/Pause Funnel Reasons. Finally, all these actions require the Edit Subscriptions permission.