Roaming in Europe on a new prepaid card

A few days ago I activated a new prepaid number ($ 35 + $ 15).

I didn't manage to create an AT&T account for this number while in the US.

I came to Europe and I do not have roaming. Because of this, I can't even create a new account because I don't get text messages from AT&T.

I have topped up my account for another $ 17, but I still don't have a network.

How can I activate roaming without coverage on this number? I have internet access on my computer.

Please help.