If its not showing up when following the steps in the support document you posted from, its either not being charged by Apple or at the very least its not tied to the Apple ID you are currently logged in with and trying it find it on.
How does the charge for it show up on your payment method's statement? Unless it appears as "apple.com/bill" it would not be billed by Apple and as such would not be able to be cancelled through your Apple subscription list.
If its showing up as "Invoice2Go" or something other than "apple.com/bill" on your payment methods statement, then it is being charged directly by them, and Apple has nothing to do with it.
https://support.2go.com/hc/en-us/articles/216361917-Managing-your-subscription-