Hey @BigZ1ggy. In order to cancel your ESO Plus membership on your Xbox One, you'll need to contact the Xbox Support team, here: http://support.xbox.com.
It only lasts a month doesn't it?
Can't you just wait it out??
I was actually pretty p***ed when I got ESO plus (thinking it was a yearly sub) only to find out, or have it implied, that the sub only lasts a month.
I still need to do more research on that one but a monthly sub does sound more MMORPG-ish and like "good business" for zennimax and/or Bethesda.