LG Artcool Dual Inverter CH21 Error After Two Weeks

I purchased an LG Artcool Dual Inverter air conditioner from Hepsiburada seller Lasen with order number 426 315 151 6 about two weeks ago. Today, the device started giving a CH21 error code and it does not go away, so I cannot use the air conditioner properly even though it is almost brand new. I contacted LG service and Hepsiburada/Lasen customer service regarding this problem, but they stated they are too busy or simply did not respond, so I have not received any support or solution so far. Because the device is only two weeks old and clearly under warranty, I request an urgent solution to this issue. I expect immediate repair under warranty without any additional cost, and if the problem cannot be resolved quickly and permanently, I demand replacement of the unit with a new, fault-free product or, if necessary, a full refund of the amount I paid.