Airlines/ Airports

This is a very worst service my mother face while travelling by lufthansa. We preponed the ticket by calling Lufthansa Airlines and they charged to my Credit Card also. I also booked a Special Assistance for her and customer service confirmed me. I check 3-4 times with lufthansa. I dropeed my moher at IAD, (via United Airlines.) They handover Boarding passes upto Frankfurt and inform that there is some problem in system and we cant give you frankfurt to delhi Boardingpass. You will get from Frankfurt without any problem.
At Franfurt Airport, they told to my mother that your ticket payment is still pending and you can not board. You need to make a payment otherwise stay at Airport or if you have german Visa you can go out. She got full of stress and also she dont know English.
Thanks to other passengers who shout on Lufthansa team for misbehaving and other things. Thank god she was carrying a Credit card, I arrange in her name. She paid the amount and purchased a ticket. This thing happened on return journey. and ticket was purchased from Lufthansa websites and payment charged to credit card 3 months before. Once my mother reached to delhi she explain me everything and I called Lufthansa and shout on them then customer service figure out after 45 minutes talk that Delhi office forget to transmit payment informations and they refund payment made by my mother.
But imagine how much stress they provide to my mother and now she refused to travel alone in future. is there we can file a complaint and get compensations.