Bought new iphone but got refurbished device.

I bought a new iphone 11 pro max this year June 13 from South Korea.

But after few months I knew that it's a refurbished device cause the model number starts with ' F ' . Recently I'm realizing that the device getting so warm after using continuously more than 4 or 5 hours and sometimes it works slowly while I use any social networking apps by using wifi.

I bought it from apple authorized store.

About 6 months remaining of the device warranty. I still live in South Korea.

I actually didn't know about refurbished device. So lately I'm here to know if I can do anything in this regard.

Have I anything to do at this moment?

Thanks in advance.