Issue solved. I called them now and successfully completed the call.

Some good and some bad news for me.

Good is that they do open tickets for the segments for more than one year from now. LAN is refusing to do that.

The bad is the price. For my itinerary LAN charges US$ 2.960,00 total and AA wants US$ 4.400 plus taxes (the guy gave-me the same price i can get on the OW website).

Also the itinerary had some little changes since that US$ 3.100,00 quotation and the prices had rise in the beginning of August so I'll do the quotation again and post results here.

Just a dumb question: if I buy the ticket with, lets say, LAN, and want to change the date of one flight, that must be done with LAN or I could use another airline, like AA?

Because they are so much better than LAN, at least on the phone.