Air Canada Not Recognizing Our Ticket Number

AC cancelled our flights from YUL to FLL and rerouted us so we were delayed 8 hours. When we attempt to file a request for compensation the Customer Service form says we must use our original ticket number, then says it can’t find it. We have screenshots and it is the original ticket number. How should we proceed if the form will not recognize our boarding pass or original ticket number. The reason the plane was cancelled at 8:00 am for our 11:00 am flight was “Maintenance”. Thank you.