My Stanley Quencher Thermos Leaked, but They Refused to Accept the Return

I bought Stanley Quencher Straw Thermos Cup 1.18 liters 1.18 liters - Sugar Pink from 'Kutupayısı'. When it arrived, I tried it without using it by looking at the instructions. The specified features were not available and it was leaking. I returned it and they replied that it could not be returned. How can a faulty product that has never been used be returned like a joke? How can such a global brand work with this company in Turkey? 'Kutupayısı's customer representative speaks as if he is scolding. As a lawyer, I will seek all my rights. I will apply to the Arbitration Board.