Updated 12/11/17: Resolved. Purchase was refunded, after abut a day of phone calls. I was finally able to extend the intended Realm, That is the good news. Bad news: the process needs improvement.
I am very dissatisfied with the absence of the Extend Realm Button for a trial realm that expired today. My only option was to purchase a New Realm. It seems very deceptive that the Extend Button appeared only after purchasing a New Realm. Most likely, my only option will be to Close the old one, and recreate and reinvite old members, to the new Realm. The purchase agreement options are not consumer friendly. The support process is extremely convoluted, as bad or worse, as during the two months of starting Better Together.
Added: Refund was possible. But a major, convoluted mess continues. While in Minecraft, as Riverboat12341, at the Store within Minecraft, purchases are directed to a different gamertag. Such purchases do show up at Riverboat12341, and not at the other gamertag. Why is the Store not seeing me as Riverboat12341, while within Minecraft, and signed in as Riverboat12341???? The programmers need to fix this mess! I spent 20 minutes explaining to the Game Tech Support person (at Xbox I think) that I could see the Realm (for which I wanted the Refund) in Minecraft, as Riverboat12341, live, real time, while we were on the phone, and not a different device logged in as the other gamertag. According to their information, what he could see, the new Realm was for the other gamertag. Not so! It was showing up on my screen as Riverboat12341.
On a different device, as that different gamertag, an old expired trial Realm still appears a 0 Days, with no Extend Realm button. Only a Renew Realm button. On that machine, and on the one above, there was a message that I am not able to re-find, about needing to make the Realm purchase at the Unknown Store. Please, do tell, what is the Unknown Store???