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I do not recall a card that charged for Authorized Users, but did not disclose the amount of the fee in the statutory Pricing Information (attached). I do recall a card that had a contingent AU fee triggered by requesting a Priority Pass account, but this was disclosed. Not mentioning a fee is not exactly the same as "free", but any ambiguity should be resolved in the customer's favor.
I would ask them to show you where the AU fee schedule is published, but I would not have this discussion with a frontline customer service agent.
If the discussion is not productive I would file a complaint with the CFPB.
https://www.consumerfinance.gov/complaint/