I also recoiled in horror reading what they told you, swimmingly (I don’t have bipolar, btw, I was just lured in by the awesome title!)
Prayers may offer some people comfort, I’m not religious but I still appreciate in a way if someone tells me I’m in their prayers because it’s basically another way of saying I’m in their thoughts. But that’s all they do - they don’t have any real world effect beyond letting someone know you’re thinking of them (positive or negative).
So, as BethRags intimated, it’s really inappropriate to offer prayers as a solution for curing mental illness (or anything else). It can and has cost lives.
I hope if you report them that the group you went to improves and gets more supportive.