New facebook account.
(or ask staff to fix it for you via help and support):
I don't know that there's a user control for unlinking a facebook account because I haven't linked mine, but every time I've seen this issue staff has had to intervene, so I doubt that there is.
I made an account merged with my facebook one but I made a mistake on the username. So I canceled that acoount and I created a new one but now I cannot merge it with my facobook account. What should I do?