Defective Vestel 55UV9750 and 43UV9750 Black Band on Screen

I purchased two televisions, models Vestel 55uv9750 and 43uv9750, 10 days ago. From the very first day, both devices have shown a black band at the top of the screen that blocks the view, and the problem persists without any improvement. I contacted Vestel customer service and the seller three times regarding this issue, and although the authorized service examined the televisions, the factory refused to acknowledge the defect. My televisions are only 10 days old and still under warranty. Furthermore, the products were introduced and sold to me as LED televisions, but the invoice (No: opt2025000000744) lists them as LCD. My expectation from Vestel is either a refund for these defective televisions or a replacement with functional models that are truly LED, along with a correction of the invoice details.