VERY RUDE STAFF AT GATES AND APP NOT WORKING ALL THE TIME WITH LATAM AIRLINES

I have a very big booking wih Latam Airlines and they have a constant problerm with therirt seat selection. Big problem with the Check in Staff, I have long legs and struggle to sit in their seats, they refuse to help me with payment of upgrade to an ermergency seat. I have nine internal flights in Argentina and Brazil with they are constantly rude to me. First in Beunos Aires and the gate staff in Beunos Aires Flight LA7508 29 June are extremely rude! They order people around and shout at passengers at the gate. Then again on flight LA 3387 and flight LA3554 to Salvador via Sao Paulo you can not do seat selection either! It is horrible they push me to the back of the plane and then they can not let me pay in for extra luggage either. The staff at check in gates do not help either as they treat you with a "no" on all your requests. Rude past the point of understanding! I spent over 4000 Dollars on them in flights and they treat me like I am a sercond hand citizen. They urgently need to fix heir system as one can check in but you cannot do anything on the app.