Bajaj Company - Complaint against service center

Sir,
My uncle met with an accident almost ** days back. He took his auto(Bajaj qute) to Anantheswara motors kollam. They gave him an estimate of ** thousand. It was kind of expected because these dealers know that he will claim insurance and thats why they replace everything instead of fixing the auto. But he was counting on my insurance surveyor to bring down the estimates.
Now, insurance surveyor(from Godigit insurance) took * days to come up with the report that the estimates of ** thousand was correct . After the work Insurance company paid ** thousand and rest will be borne by my uncle.When my uncle asked for the bill at the service center, Service manager Sham was given a GST bill of Rs **,*** and an estimated bill of Rs **,***.my uncle paid the total amount and took the auto.
A week after that, the car break down again, When he towed the auto and went to the service center, they said that there is work worth ***** rupees and that it has been done.There is also a problem, the engine has providing a sound, and needs ***** thousand rupees to rebuild it.

my questions?
*.Why did the engine complaint the two year old car even though it was fully serviced?
*.**,*** rupees will be charged for hitting a bumper on a auto worth *.* lakh rupees why?
*.Why did you not give the GST bill instead of the estimated amount of ** thousand rupees?
*.Why did it take two and a half months to get the accident auto built?

Auto is not bought for the sake of luxury, but for everyday life.