Now I'm just checking.........
Is your mobile phone's software up to date (older mobiles will no longer run the app as they are not being updated) and are you using the latest app version.
Remember that the default setting for the app is the EN server.
To access the US server you must tap on the EN flag and then you should gain access to scroll through all the different country servers until you come to the US server, select that one and with some luck you should be able to log on.
If you can't log on then send another ticket into Support.