Samsung S21 is modified ?

[Vasare]

Dear all, 

I bought Samsung S21 five months ago. From official Samsung store.

I had a problem, that my phone  Samsung S21 stuck, I could not turn it off/on.
Took it to Samsung Official Servise,  and the said that my warranty is not working, because my operating system is ilegaly modified. Also they said that they need to change the motherboard of phone, that costs, like a half phone now.
I havent done any, any kind of "modifications" on my phone, it has everything like it had when i bought. Plus some apps from Google app store, but such as yahoo mail, gmail, facebook, mesenger and etc. Nothing special with my phone was made, except photos and texting, calls. I even dont use it for my work.

Maybe someone had problem like this?

Please, explain me how could this happen? How that modification came to my phone?
What do u think, how can I protect myself from paying? Or it is no way to prove that i havent done this?

Thank You , waiting for any ideas, please

[GMEDIA · Accepted solution]

Yes, rooting will void the warranty in most mobile devices. Rooting has the potential risk of bricking the phone rendering it useless. You can check this simple way run Samsung Pass application if it's open than your device is not rooted.
Check this link for more information; https://docs.samsungknox.com/admin/knox-platform-for-enterprise/faqs/faq-115013562087.htm