HELP - How to get a business page to join a group you are already part of?

[Overseasmom100]

Can anyone help with this please...

I am an admin on a few business FB pages say A, B and C (mainly helping friends with their social media for a bit)
So page C Ive tried to join a group but when it asked who you want to join - it lists A, B but not C - so I cant join a C

Has page C got an incorrect setting somewhere?
I've spent literally all last night trying to favthem out how to do this...
any ideas anyone???

Is it to do with how new your page is perhaps? although it's been live for a couple of months only has a few likes (19) but that's why I want to share to other groups

Anyone??