Totally agree with you, and will take your advice on sending a complaint to Lufthansa. Of course Lufthansa will not give a straight refund for the missed flight (the way the agent documented passenger absence was no-show) so according to their system, parents just did not show up and the flight carried on. No fault by Lufthansa. They offered a voucher valid for 1 year.
Gonna try and rebook, and if it happens again, backup plan to book with another airline and accept that Lufthansa will have stolen $$$$ for their stupid mistake.
Ill update with the end result.
