I do sympathise and maybe Lufthansa should have made an exception and offered assistance in this case.
However, as I see it, the very few Lufthansa long-haul services ex-DUS are intended for the local market rather than those from overseas who might be intending to use DUS as a hub.
In any case, this non-stop flight is seasonal. It is withdrawn effective October 25 and according to luftansa.com, will not resume until summer 2016.
I do hope it works out in the end.