Even when you think you have a clue, having read these threads and write to LH or ring them, they all come up with the same non-accurate answers as usual. Guess if they don't come up with a nice offer (I would even happy if they claim a service charge for that) then you should calculate the total claim and you may raise a Mahnbescheid which could lead to a case at court then.
I have some tickets only used one way (cause plans did change or even once I mixed up the correct return day and showed up 24h late ) but to compare it with the flown trips it's nearly unrelevant, so clearly we can demonstrate this was never done by intention.
Best of luck - and I am currently trying to get my tax back as well
muc_flyer