Want to set up an international plan but already aboard

Accounts are blocked from outside the United States 

Hi, what do you mean by "blocked"? Are you saying that I can't use an att mobile plan (including international plans) from outside the US, or that I can't access my att account online?

He is saying you can’t access your account from abroad. You can of course add an international plan if you are eligible but that will require contacting customer support. Do you have postpaid or prepaid service? If prepaid, prepaid can only roam in select European and Caribbean countries. 

Yeah there's a lot of missing information in your original post that might help us help you. 

1.   Even without a roaming plan, if your phone was set up for Wi-Fi calling you would be able to call and text and receive text message and phone calls from the USA over a Wi-Fi connection for free. There are a handful of countries which do not allow Wi-Fi calling.

China, Saudi Arabia, India, Turkey, Israel, United Arab Emirates, Vietnam, Pakistan, Cuba, Iran, North Korea, Sudan, and Syria.

2.   If you just signed up for at&t, there may be a 60-day restrictions which will not allow you to roam with AT&T postpaid even with international day pass.

3.   Prepaid has limited roaming.

https://www.att.com/prepaid/static-pages/intl-travel-add-on/

If you are in one of these countries and you have AT&T prepaid you should be able to log into your prepaid account as long as you know your alphanumeric password and your PIN code.  This would allow you to add the $35 required and select the prepaid roaming add-on.  

4.  If you are postpaid and took your phone out of airplane mode you should have received a text message informing you that international day pass was added to your line to cover your roaming charges. International day pass charges you $10 on any day you use service outside of the USA. The limits of this are your domestic plan. Not all postpaid domestic plans are eligible.