Mytrip Ruined My Travel Plans Due to Unexplained Ticket Cancellation

We purchased round-trip flight tickets from Istanbul to Jeddah and back via Mytrip. Due to my spouse needing to travel on a different date, we didn't use the outbound ticket. Today around 16:00, my spouse went to check-in for the return flight from Jeddah to Istanbul. No one at Jeddah airport assisted, and they said our ticket was canceled. Mytrip didn't inform us about the canceled ticket at all. Because of them, we had to buy new tickets for ₺18,000. I will complain everywhere necessary. Our reference number is 4Y6WGB. When my spouse found out they weren't allowed on the plane and their ticket was canceled, we immediately contacted live support. They said they couldn't do anything. We bought a round-trip ticket, missed the outbound flight, and they canceled the return! What does this mean, and why wasn't I informed? Mytrip, you are a disappointment!