KLM complaint: Payment for SEATS

Dear SirsMadam,

Myself Sridhar Krishnamachary and my wife travelled to Amsterdam on 28.10.2022 by Delta operated by KLM. My ticket includes the seat of my choice and the same was selected while making my bookings and was ed.
On the day of my departure when io went to drop my bag, the official at the counter insisted and pressurized me to pay once again for my seats, in spite of telling her that my fare covers the seats.
They were not prepared to my reasoning; they made me wait for an hour and collected the money for two seats.
Today i called up delta office and they suggested that i should call KLM office, i did call them and explained to them whole situation, the person who spoke to me on phone said that they cannot refund my money, when i questioned him, how anyone can collect twice for the same seat, he said he is sorry for what had happened.
I wish to make a complaint and to reach the higher officials and bring to their attention.