OnePlus - Faulty or Not properly working Mobile Handset

I bought a OnePlus device almost *.* years back and till date, the device is not working properly. It has got a notifications issue from the third party application. Despite rigorous complains till date, the issue remains unsolved. The device has been submitted to their Service Centre more than * times. Even the hardware has also been replaced to solve it. There was an instance that device was kept with the Service Centre more than * days to thoroughly check the isue. But no solution. Also to avoid the software glitches, I have shared the system logs with the team sitting in China *-* times but I never got the satisfactory answer or solution to this issue. Even team from India isss trying to solve the issue but never got the solution, every time both the team keep on telling that wait for the next OS update and it shall solve the issue but it never got solved. I am also attaching the conversation which took place between China OnePlus team and me