Paid and pre booked seats in advance and changed by airline with no warring or remorse!!!!

We Pre-booked and paid a premium for front row seats for my mom flying from JHB to Cape Town due to her having had 3 hip replacements and not been able to bend her legs properly. When trying to book ed her in online they have moved her seats to row 11 ?????? After calling the call center they can only tell us that the airport changed her seats and there is nothing they can do to help but if we want to complain we must send an email and they will respond with in 48 hours.. I have paid for a seat and i want my seat and we cant wait 48 hours due to her flying in the morning.