> Callers from legitimate businesses treat me like i’m questioning the moon landing when I tell them I’ll need to call them at an official number.

Not to justify their behaviour, but: most businesses are not set up to allow for callbacks or they're set up to actively discourage them. For example: they may be contracting out to call centers or employee performance may depend upon making a sale. My situation is unique since all calls our handled internally and my performance is not based upon making a sale.

That's said, the current situation pretty much dictates that a secure option should be offered to clients.