My impression is they're getting confused with what you need. You don't need to ask about when you're getting paid. Deal with one issue at a time.

You need to say, "I've received a Fully Favorable SSDI decision. I have my bank account information that I need to have updated." Then hand the rep a voided check, or a printed copy of the account number and routing number. If they say they can't help you, ask for a supervisor.