How do I get foreign exchange out of Angola?

Hi all. I have an Angolan client who deposited USD in his account in Angola and submitted all the paperwork to send it to my company to pay a long overdue invoice. This was 11 weeks ago. The manager of his branch (BAI) has told me ion several occasions that the money has been sent, but his last message was that the director of operations at head office was handling the transfer. No one at head office will come to the phone, BNA aren't saying anything and UKTI have said that there is nothing they can do. I can possibly get the Angolan ambassador to the UK of the Angolan minister of education to intervene (my client is a university), as they were involved in the early stages of the transaction, but that might take a while and I worry also that it might be counter-productive. I would appreciate any advice or help as if the money doesn't land soon, for various reasons I will not be able access it. - Is 11 weeks normal? - Will I have much longer, realistically, to wait? - Am I missing a trick? That is, if I hire a local lawyer/fixer, will that help..? Thanks hugely for any advice FB