If the lawyer doesn't obey the contract rules?

After my I-140 got approved, I emailed and called the lawyer many times. No respone even I ask him about the last payment. Half month later I received a bill. After he received my check,he sent me the checklist for the I-485 application and told me someone in his office may help me with this I-485. Until now nobody in his office contacted me. I sent him email to ask. No response. This lawyer is an American.

So could you please give me ideas? Thanks