Just because they don't have IT set up to tell them whether the pax has been informed, doesn't mean it isn't their responsibility to make sure it happens. The fact that LG had your direct contact info too is just the icing on the cake.

LG has an agency agreement with priceline which stipulates priceline's responsibilities, including informing pax of schedule changes. If priceline failed to fulfill it's responsibilities, that's LG's problem, not yours.

What really annoys me about this story is that LG refused to refund. Schedule changes happen and agencies make mistakes, but I've never heard of an airline refusing to refund a ticket that was schedule changed 24 hours. That's simply unacceptable.