find the device a purchase was made from

There really is no way to tell which console/device the purchase was made from the best thing to do is to have your son change the password on his account and not give the new password out to anyone. If his profile is still on the other consoles changing
the password on his account would then require them to enter the new password if they were to try and sign into his account on their consoles and if they do not know the new password then they would not have access to his account.

In addition i would recommend to change the home console back to his own console if this was set up to another one and change the security details.

http://support.xbox.com/contact-us

This is going to be the best route here. When you find the rascal who did it, give them a good ticking off too!

Definitely have to contact support to figure that out.

You are advised not to share your account data in order to avoid issues of this nature. Even if the purchase was made through a different console that proves nothing if the account in question was used in three different consoles with the owners consent.

That being said for billing and purchasing issues contact xbox support: http://support.xbox.com/contact-us