"I'm sorry you feel that way" is a canned non-apology, worse than a canned apology. At least a canned apology admits fault.
I wouldn't want to get into a call with someone with that attitude. If I'm quitting because no consideration was given to me or my work, and the first response I get shows no consideration to me, my work, or even acknowledge my list of grievances, a "quick call" is the last thing I feel like getting on.
In fact, even that word, "quick", is insulting, because there's no way this is getting fixed with a "quick" call. "Quick call" implies the grievances are minor. More insults.
No it's not! There's a support forum right there, use it. The only reason they want a call is because they want to try to grind down the volunteer while having everything off the record.
Talking face-to-face about what though? Apparently it's about "what you're struggling with", not "what we fucked up". There's a complete inability to admit any fault in this message, so the conversation is already primed to be bullshit. I would expect such a conversation to be a waste of my time and would never agree to it.