Looking for some assistance here.

I made a reservation on AA.com with all segments flown by LAN.

My original booking had 3 segments:
LA 751 GRU-SCL DEC 2
LA 455 SCL-EZE DEC 6
LA 6451 EZE-GIG DEC 11

Now, the reservation only has LA 751 and LA 455. I called AA and they said that LAN dropped the last segment and they no longer serve that route (presumably when they fully became LATAM). The flight still exists on googleflights but it is listed as TAM Paraguay, which is assume is now just a full separate legal entity. AA said they cannot put me on that flight because TAM is no longer in Oneworld and that I should reach out to LAN. I emailed LAN and they said that the problem is AA's to resolve since that is where I ticketed the flight.

If I judst book that last leg separately, the fare is over $600, which is $200 higher than I paid for all 3 segments originally. What options do I have other than getting a full refund from AA?