Turkish Airlines Doesn't Want To Refund My Money

Turkish Airlines doesn't want to refund the amount I paid for emergency exit seats for 2 pax. They have conflict on their Mobil application. You can't pay flight and seat selection at the same time.. Though, they charge the amount. They could refund fee only for one seat but they are claming that they refunded for 2 seats. My bank received refund only for one seat and I sent them these documentations, but they do not wanna prove their claim with the financial documents those I requested. Simply, my money disappeared and they don't wanna do anything. It's a shame. Though, they claim that they are the best airline on the world.