problem in switching onn the smartphone

Phone does not turn on at once it takes around 5-15 tries and after so many times it switches onn.

I purchased this device(iphone 12 mini) at november 2021 and from january i started facing many problems i don’t think this is a software problem because previously when i have complained they told me that there’s no problem in your software so please give me valid explanation for the same and this is my humble request to change my device