That doesn't make sense... like i said, the linked Starbucks account is already deleted by Starbucks (their fault), so Starbucks rep can't even look up that linked Starbucks account, so there is no way for them to unlink something that doesn't exist on their end.

I had same situation with Delta-Starbucks linking.... Delta was able to manually unlink the linked Starbucks account, and once they did that, I was able to link new Starbucks account with my Delta account.

I am sure there is a way for Marriott to manually unlink it, maybe you can find an IT staff to do it?

Or perhaps I can create a duplicate Marriott account, and link my new Starbucks account to that duplicate Marriott account, and then merge the duplicate Marriott account to my current marriott account? the new link would overwrite the old link if i request it, right?