jcamp028 wasn't very clear in his statement. It was the LX flight FRA-ZRH that was cancelled.

But, all aside, I'd check the exact landing time in ZRH. If (just a tiny bit) less than 3hours than your scheduled arrival, you're due nothing. If between 3hrs and 4hrs, 300€ each, and if above 4hrs, 600€ each. You'll definitely have to fight for it, though.

With you stating the next flight was 3hrs later, and FRA-ZRH definitely having a lot of flights per day (so the next one hardly ever is 3+ hours away if one gets cancelled), I could imagine it was a bit less than 3hrs quite easily, and the final arrival time was below 3hrs. Which would make the whole discussion here pointless