No respect for senior citizens

My parents senior citizens where left by the bus (NB not plane, bus) after boarding which then resulted in them being left by the plan. My sister had done my parents bonding pass online and took them through the gates to board the bus which will take them to the plane. The lady took my parents through the gate and my sister left to go home. An hour passed an my sister gets a call to say my parent missed their flight. How the story unfolds My mother a plus size elderly woman gets left behind by my father the customer service lady on the way to the bus, my father gets to the bus but refuses to bond because he's still waiting for his wife. My mothers and father are then left behind by bus which result in them missing the plane. Complaint If someone passes the bonding gate I believe there is no way that person can miss the flight. Customer service lady with a horrible attitude when asked for assistance only had 3 words to say 'late is late ' and refused to assist us in any way, refused to call the supervisor and my sister way told to book again and would forfeit the monies on tickets purchase. The sad part is the ill treatment of our parents, the hurt and how they wanted to board a bus cause money has been lost. We had to beg our parent for us to rebook with our money. May someone please assist with the way forward