Go on to prepaid self-serve. Print out your profile including the acct number on the opening page after you have signed in. That's enough info for any other provider: phone number, acct no and your particulars.
They ask for a bill because a lot of consumers get confused when you tell them the specific information needed. What Bob said will suffice. You really only need to know your account number as everything else they would require you should know (like your name/address, if even asked for it)