Well I seen this being sold and I figured I'd share since its not hard to do.
If you think some one called on your Xbox account visit the following link.
https://support.microsoft.com/oas/default.aspx?tp=il&st=1&wfxredirect=1&sd=gn
Sign into the Xbox account that you are concerned about.
Click on Open.
They will show here
http://gyazo.com/d3960725c1ee10ae81aeed1f2eb4fe90
If you have any closed cases they would show under closed like this.
http://gyazo.com/933117af69c5e9a7bfa194f0b7af5ace
The SR # is the number located next to it.
This is perfect for buying a Xbox account you can see if it was ever reported stolen etc before you purchase it.
Edit:
UA's don't show always lately for some reason but if someone did call you would get a Verify me code issued to your email or phones on file.
Something to look out for.
If you think some one called on your Xbox account visit the following link.
https://support.microsoft.com/oas/default.aspx?tp=il&st=1&wfxredirect=1&sd=gn
Sign into the Xbox account that you are concerned about.
Click on Open.
They will show here
http://gyazo.com/d3960725c1ee10ae81aeed1f2eb4fe90
If you have any closed cases they would show under closed like this.
http://gyazo.com/933117af69c5e9a7bfa194f0b7af5ace
The SR # is the number located next to it.
This is perfect for buying a Xbox account you can see if it was ever reported stolen etc before you purchase it.
Edit:
UA's don't show always lately for some reason but if someone did call you would get a Verify me code issued to your email or phones on file.
Something to look out for.