A non-refundable deposit fare is priced lower in exchange for you giving up the deposit if you cancel, and usually accepting a change fee.
For price protection it introduces a matching rule people miss: a non-refundable fare can generally only be claimed against another non-refundable fare. Finding a lower refundable price does not produce a claim, because the line treats them as different products.
Check which you booked before spending time on a claim.
