My tickets are cancelled without notification

I bought tickets Valdivia–Santiago–Madrid but LATAM Express went on strike. It's ok, I was going to take a bus to Santiago and use my Santiago–Madrid flight.But it turned out that because Valdivia–Santiago was cancelled, LATAM also cancelled my Santiago–Madrid flight and sold it to another person!!I wasn't even contacted by the airline! They just silently trashed my tickets and I learned about it on my own, 3 days before the departure. Of course I can't find any good flights available on these dates.LATAM should not cancel my Santiago–Madrid ticket automatically without asking me first. Please fix your software or whatever caused this problem. And add automatic notification when the flight is cancelled.