I want to sell my old iPhone 6 Plus and get a new one. I’m living in Bangladesh and I’m a student. Can you help me?

I want to sell or change my old iPhone to a new one. Because it’s not working good I need a new one. Actually I am from Afghanistan. But I’m living in Bangladesh Chittagong province. I’m studying at Asian university for women. I’m a student and I need a new iPhone urgently. Can you help me in this issue. Can you give me a discount for buying a new one or give me a gift?