Samsung — SAMSUNG A50 Motherboard Quality Issue

I bought a A50 mobile 7 October 2019 for my uncle. After 1 Year and 2 months of Normal usage, one day while attending a call mobile started restarting automatically and it kept restarting and shows samsung logo. This happened multiple times. I gave the mobile in Samsung service center, after a day they told its booting IC issue you have to change the motherboard and it costs Rs 9500. Reason they mentioned is over usage of memory. Firstly, its not overused and I don't understand how memory usage resulted in Hardware issue.
I asked how they identified the issue, reply was since it is not booting so we need to change motherboard and they dont have any equipment to identify the faults.
Few thing I dont understand here,
1.Mobile never fell down not even once.
2.Motherboard completely sealed.I cant touch it and never gave in outside shops for repair.
3.Does Service center just replace parts? Why there is no equipment to identify issue? Just money is motive?
4.Replacing motherboard means buying new phone. We know that new Phone will work. is that the only solution you have for mobile repairs?

Definitely there is a quality issue in the product. With normal usage and no physical damage how come motherboard gets an issue?

Replace my mobile with quality one or refund my money. its 18, 000Rs mobile.

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