My Attorney Represented The Opposing Party In Previous Case And Did Not Disclose That To Me.

This case is in California. I hired an attorney to represent my husband and I in a tenant eviction case. We had tenants that decided to stop paying rent after 3 months of moving in, so we sought this attorney’s legal representation. He was one of the worst attorneys I could have had. He seemed to always scramble last minute when a motion was due. He was horrible at explaining the process, which made our stressful situation even worse. I have multiple emails (documentation) complaining to him about his lack of responsiveness. When we finally got to court, he had no strategy! His initial strategy was to tell us to go negotiate with the defendant. As absurd and maddening as that was, he then encouraged us to settle. The case ended with us agreeing to not seek back rent in exchange for the tenants to move out in 30 days. As a result, our losses were in the $40K range. Prior to the court date, the attorney led us to understand that we are entitled to seek back rent. Months later, I was contacted by an attorney that was seeking information about those same tenants that we went to court to evict. In speaking with him, he informed me that my attorney had previously represented those same tenants in a previous case. He even sent me the documents with the case number for proof. So now I have physical evidence if I want to go after my attorney. What is my best recourse against the attorney? Who do I contact and what do I ask for? I want to recover the money that he should have tried to seek for our lost back rent and/or his attorney fees.