Are you the only member of the FC? If so, have them help out. They're ostensibly being held prisoner as well.
That said, it's absolutely stupid that an FC leader can block FC members from accessing something they paid for. I can understand blocking usage of amenities such as company chests, merchants, etc., but this is one of the most absurd design oversights i've ever seen.
Actually it's more than a design oversight since they had to intentionally add it. WTF?