Faulty iphon 13 pro max

I bought iphon 13 pro max on 26 of Dec in 2021. And I’ve been using this for 3 weeks, it seems it is faulty product. Firstly, when I call with speaker, the sound cut off so ppl can’t hear me. Secondly, iphone recognized I am pushing volume up button when I am not touching phone at all. So the volume goes to max and phone is vibrating. Lastly, iphone turns on itself even no one touches it. I am not keeping receipt and box. How would I do?