OnePlus Nord 3 Mobile Network Issue

I purchased a OnePlus Nord 3 smartphone from Media Markt’s online store. After using the device for a few days, I started experiencing mobile network connection issues. When I contacted Media Markt customer service, I was unable to get proper assistance. Instead of providing support, they told me that since the device is covered under a distributor warranty, I need to contact the distributor myself and even find their contact information on my own.

However, the website stated that the phone comes with a brand warranty, which is misleading. I am not requesting a refund, but I do want a replacement unit because:

The phone’s price has increased since my purchase.
I have already spent additional money on a case and screen protector.
I expect Media Markt to take responsibility and provide a quick resolution. I did not anticipate such a lack of after-sales support from a well-known retailer. I request immediate action to replace my defective device.