Ok. Instead of having a replacement, the shop gave me a full refund. All the units they got, including the one they were supposed to give me for replacement has either those lines or more spots. I opted for a full refund instead...

Yesterday, I looked for another shop. I found one selling for the same price. They didn't have any 64GB stock, the store made a reservation for me, and was told to return the next day. Today, I went to that shop. Guess what? NO DARK LINES AT ALL as well as those bloody dark spots!!! I'm very very happy! Yeepi-ka-yey!!