Lost Sim card

I lost my new sim card so I been using my old sim card with my old number on it which is connected to my old account. I want to cancel my new account because I dont want to pay for two accounts. The problem is I can't access my new account because I dont have access to the text messages for a pin number to sign into the account. The account is on auto pay also,so it will continue to charge my card if not cancelled. i know the phone number but it just wont let me sign in because I need the temporary pin to continue. I also do not have access to a at&t store right now.