Hello @zschwert
Welcome to the Community Forums! I appreciate you taking the time to get this resolved and understand your concerns! I would be more than happy to help.
Combining two or more services is great and can take 2-3 billing cycles to apply. Once it is in effect you can find instructions on how to login in this helpful article. The method will depend on the type of accounts combined.
I noticed you mentioned you are currently out of the country. Currently myAT&T does not work in certain countries, so this could be why you are unable to log in. I will be sending you a private message to your forums inbox to provide more information. Please be on the lookout for it!
I hope you have a wonderful time abroad, and please have an amazing day!
Jessica, AT&T Community Specialist