Typical of LX, since it was a technical failure, under EU261 you are entitled to €600 compensation each plus, full duty of care, as you have gathered LX do not respect EU261, so you will need to fight, DoT complaint is a good idea anyway & then explore other options. Was your flight just to ZRH or onward ? I note your location London, if your routing was there, UK261 applies and MCOL is easy cheap & very effective.