want to delete a duplicate group from iMessage

I added another iMessage group with the same name - one number differs ( cant remember how I managed this) and now I cant tell the difference between them when they are offered via predictive texts until the name turns blue. the group I want to delete altogether is green (one number doesnt have iMessage active).

the group I want to delete/remove - I tried removing each member via group info but it doesnt allow me, I dont get any options other than sharing location, members' contact details, etc. I cant seem to remove myself but that might be bc I created the group. I definitely cannot remove anyone in this 2nd group. In the original group, I can remove people.

Basically, when I share a webpage, photo, etc I start typing the group name and two groups appear, both in blue suggesting it's using iMessage but when I select one, it turns green. if I notice (I often dont) before hitting send, I can delete the name and choose again. I have two groups with same name - one member has a different contact number (that's why I want rid of it)

Anyway, I've looked online for an answer and apparently it should be straightforward to remove people from the 2nd group. it isnt. I can delete the group conversations from iMessages list on MacBook/iPhone but the group reappears next time I share something.

Ideally, I simply want to go somewhere that shows me all the groups ever created so I can delete one, or remove me/members/everyone from the group.

I forgot to take screenshots. I will the next time it happens.

I have a MacBook and iPhone.