customer taken hostage / consumer rights violated

We booked return tickets to Brazil (family with 2 young children). On arrival in Brazil (28.08.23) we received an email informing us that our return flight/route had changed. Instead of flying via Frankfurt to our final destination, the new route is via Lisbon. On arrival at the airport (11.09.23) the airline found that we had been registered on both routes, i.e. Frankfurt and Lisbon (booking error). The airline (LATAM/LUFTHANSA) refused our boarding because of this situation and asked us to contact Mytrip so that they could correct their error. We've been stuck in Brazil for 3 days without any help or assistance whatsoever, and have spent the last few days contacting Mytrip, which always asks the same questions (call centre in India) and asks us to make the changes ourselves with the companies. (which is not correct and is not the consumer's responsibility) We contacted the companies who cannot change the tickets because Mytrip is the contractor! We telephoned the call centre several times and after 3 days they offered to change the flights for a fee of 3,000 euros! (costs for 3 new tickets plus taxes) to correct an error they made themselves! Absurd statement, given that the error originated with Mytrip. The company Mytrip is using the distress and desperation of consumers to *****ulently ****** money from them to carry out basic procedures which are fundamental consumer rights and which are free of charge. We have hired a lawyer and have requested an emergency procedure before a court in Brazil in order to force the company to assume their legal responsibilities.