These situations are one of the reasons I always strongly recommend getting any settlement offer on paper (or at the very least e-mail) before sending any money. Sadly, in any case, they will generally not send the release letter in any way other than through regular mail unless they had promised otherwise beforehand. As I've said lower, your best bet would be to call the Ombudsman, inform them of how the agents have acted towards you, of the offer that was made, supply any proof of payment required, and hopefully she'll be more reasonable.
Good luck!
~Masked_Agent