Pay for Groove Music with 12 months upfront ($119.90), which already saves you a month compared with the month by month option and get $35 of Microsoft Store credit.
This credit is good for digital Music purchases, Movies, TV series, Games and Xbox Games, Apps etc.
The Groove Music app works on Windows 10, Xbox One, Windows 10 Mobile, Windows 10S, iOS & Android devices and via the website https://music.microsoft.com/
Enjoy :)
How exactly do you buy a 12 month music pass? All the links I get just offer me a free 30 day trial and then $11.99 per month.