Samsung — Samsung A9 Galaxy - Service center not repairing

I have visited Samsung service center (Ramdas Sharma complex, 1st floor, Hoshiarpur market, Sector 51, Noida) 3-4 times in last 3-4 weeks.
Earlier my device (Samsung A9 Galaxy) was frequently getting shut automatically, so service center told that they need new battery to troubleshoot, which may take 10 days. I wanted to save data on my phone, so I felt not formatting. But they said they will get new battery and if doesn't work out then formatting phone will be last option, which I agreed.

I waited for 15 days and went there again, now they said battery is not available, so this device can't be repaired. Now I don't know what to do?

This was working fine till last month, now I'm surprised that it can't be repaired this phone is completely dead? I need some solution. how come such expensive phone can be dead in 2-3 years and Samsung can't repair?