On this page where it pops up a support window, https://support.stripe.com/?contact=true (you might need to be logged in to see it) there's a dropdown with various choices, and the Chat and Call buttons get enabled or disabled depending on what you choose from the dropdown. In the default state with no option chosen, all 3 buttons are grayed out, but a lot of the options seem to enable all 3 buttons.
They don't have it 24/7. That's part of the answer.
But that kind of phrasing leaves a big gap.
Do they offer it during some hours? Which hours? Or do they offer it never?
There's a big difference between "call and chat are only extended beyond business hours for certain issues" and "call and chat are only ever for certain issues".
Are you just trying to say "we're so short staffed, there's no one to answer your messages, let alone your calls?"