AA did similar thing to me a few years back.
I booked IAD - SJU - SVG with a return in 10 days
When AA canceled the SJU - SVG leg the flight became
IAD -SJU with a return in 10 days. AA had not contacted us.
When I called, AA claimed they were going to call us or try to get us on another flight.
I had to cancel everything and start over.