When I test “Ok Google, please call [business name]”; I get a response “It looks like there is no phone number registered for [business name]”. She is recognising the businesses and repeating their names correctly, and they both have phones registered (for 5-10 years now), but it still won’t call. I also checked that both have their checkbox enabled to “Accept Google Assistant Calls”.
Google offers this feature free of charge to both businesses and customers to help them connect with each other. However, it’s not rolled out in every country.
Appointment bookings with Google Assistant are only available in the United States at the moment and not to all business categories.
I don’t think your businesses are supported by Google Assistant Call Function. As you said you enabled “Accept Google Assistant Calls” and Google Assistant recognises the business names, meaning that feature will come in the future.