Shein Order Quality Issues and Unfair Refund

I ordered from Shein, and my package arrived in 9 days without any issues with the delivery time. However, when the courier arrived, I was unexpectedly asked to pay an additional ₺620 at the door. I felt compelled to pay without any explanation provided at the time. Upon opening the package, I discovered that the quality of the items was extremely poor—the dress was so sheer that it was see-through, the T-shirt fabric felt cheap, and the zipper on the bag was already rusted. When I requested a refund, they said they would only refund ₺552. I paid ₺620 at delivery and ₺953 at the time of order, so this is unacceptable. How am I supposed to return the items, and will I also have to cover return shipping costs? Please assist, or I will file complaints wherever possible.