I would raise a formal complaint with Zen saying they have no idea what they are talking about and have not progressed the fault investigation to a satisfactory resolution, the LLUMS case was not completed or just ignored. Overall it gives a very poor impression of Zen support. Have you considered emailing the Openreach CEO (email address has been posted on various forums) giving a brief description of the problem. This has been known to get results when other routes have got nowhere.