Travel agency says flight cancelled. Airline page says flight active. What to do?

I recently booked international travel for my family. My wife and kids tickets were fine, then the travel website sent me a notice they their return flight was cancelled and that I needed to request cancellation and a refund. However, I’m also on the same return flight with them, but one of my kids and I are leaving later, and apparently our flight, the same exact flight number, isn’t cancelled. What do we do here? Are there any rules about international flights being cancelled by the airline? Aren’t we supposed to get booked on another flight?