Just ring them up and ask to cancel.
It sounds like they didn't bring this up as an option, but neither did you ask for it.
Just ask them outright for a full refund.
(Note: you can't buy travel insurance, after the fact, which you then use to "cancel" your otherwise non-refundable ticket. If insurance could be bought in this manner, then EVERY ticket becomes refundable, and only for just the cost of travel insurance which you purchase purely to claim a larger amount of money back.
And, besides, you don't need to rely on insurance to cancel in these circumstances (material 24 hr change to your flights)