Hello @Es351 ,
Welcome to the community,
Not sure why you cannot use My EE in the US, do you mean the app? Need more information, not enough to go on.
If you were wanting to use your phone, you need to have roaming, call abroad and premium calls enabled to use your phone and sim, and if on pay as you go, need enough credit.
To contact EE customer service dial 150 from your mobile phone or ring customer service for free using Skype or another phone: +44 800 079 8586 or +44 800 956 6000.
