SIM card data only plan

I have my own device and no AT&T cell phone whatsoever. I got a $50 prepaid data plan and have a modem for wireless data. When you go to www.paygoonline.com to register the phone you can log in and do all the admin stuff you need, check balance, etc. it needs to send me a temporary password via text to that SIM card ... so it is not in a cell phone so I can never get passed this step and calling support did me no good. They told me to stick the SIM into an AT&T or other unlocked phone to receive the text. Well, I do not have one of those phones. So what do I do? I cannot pay the bill, refill it, check the balance, or anything! Please ... anyone out there that can help!?!?!? Thank you! I am beyond frustrated.