Momondo Flight Booking Failure - Unconfirmed Ticket Cancellation

I booked two tickets for a family trip to Europe through Momondo months in advance and thought everything was fine because I got confirmation emails. When we got to the airport, the airline told us that the reservation had been canceled weeks ago without my knowledge. It was stressful and embarrassing to stand there with my daughter and not have any seats. I had to buy last-minute tickets directly from the airline for more than $1,500 more to make sure we didn't miss our plans. Momondo never gave me a clear answer or my money back, which ruined the start of our trip.