Standalone Data Only account

I had an old standalone data account for my iPad. ATT discontinued it and, as I needed a data account, I was able to reach an agent who switched the account to prepaid. The whole process took over three hours and I now have data, but cannot access the account. I do have the account number. The agent told me that I could register the prepaid data account on My Att as a separate account, but I have been unable to do so. Neither the old User ID nor passwords work. I need to add an additional ipad to the account, but have been unable to do so because I can't access anything. I may need to upgrade the account, but as I have no access, I can do nothing. There is no longer a phone number on my iPad. I am afraid that if I try a hard reset, I'll need to create a new account while the present one is still active. Any help would be much appreciated. Thank you