Hi mreitas,
I'm sorry to hear you are having issues with access to your online account. You may have to reach out to our tech support to have your phone numbers unlinked from the old account and set up to activate from the new account.
You can also try and register for a new account by going from your wireless phone to http://www.att.com/reg and trying though there.
You will need to be off a WiFi connection and connected to Celluar data in order for the above link to work