Poor customer service.. and refusing to settle the bill

This company has poor customer service. My car had a mechanical failure and i took it to BMW. They only settled 600 out of 3700 and refused to settle the labour as well. Why must i be the one paying for the labour of the part they have paid and they refused to pay for the other parts And number 2 why should i pay for a part that broke down while it was not broken down due to wear and tear. Why did they agree to insure a second car well its extended warranty obviously when i bought the car it did not have any problem. This is daylight ******ry. No one contacted me and informed me in simply language why they dont want to pay except that i get an email which is not straightforward as to why the bill is not paid. Does ths mean everytime i claim for a part i am gonna have to pay by myself because a new part was needed. Why are they expecting the dealer to fix the car without putting a new part then if it requires them to do so.