DOA - (Dead on Arrival) ?

Hello, I will try to tell you my problem.

I buy (30/04/19) an iPhone XS Max from store "Kotsovolos" in Greece. I open the pack (03/05/19) and after a few minutes when play with it, I see that in the metal has a very small mark on it. That's it, from that point I have big problem from the store. They did not take it back and they say that I must give to there Service point, with a note that "the iPhone has a mark on it, from the enclosing box and the costumer needs a replacement" then sent to authorised delegation in Greece to "Infoquest" . After 15 days I have nothing hear from them, I still waiting for there decision, if I did the mark or not, to the "metal surgical quality" ! The 7 days DOA is not working for me ?

I sent a form to "Ombudsman of the Consumer" here in Greece. Can anyone give me advice, how to react from now on ?

Thank for advice.