City responsibility on Sewer pipes

[John D.]

My plumber found out by inserting a camera that my city sewer pipe has roots in it which is causing my house sewer to back up. The roots are from the tree which the city has planted on the sidewalk. I filed a claim with the city and the insurance company contracted by the city responded that "A public entity is immune from the liability in the absence of having been place on Prior notice of an issue. The city has reviewed their records and notes no prior complaints/service requests for tree root issues at this location". The cost is approx $9000 to replace the sewer pipes. Any ideas on how should I respond to the city and other options I should explore?