Non-solicitation clause

Hello sir, I am a software engineer. I worked in a company for 4.5 years from 2014 to 2018. In 2018 I left that company and joined an MNC in Noida. I was in touch with an indirect client from that previous company and came to know that they had a vacancy. So I talked to him and joined that company. Now my previous company has proceeded with a legal case against me as there was a non-solicitation clause in my appointment letter which I somehow didn't check. I have tried to talk to my previous company but they are saying that they will take the case as far as it goes. What can I do in this case? Point in my favour are: 1. I joined another company and worked there for 10 months before joining this client company 2. This client company is not a direct client of my previous company. But a client of a related company. This related company and my previous company have one director in common. But my employment agreement does not mention this related company. Please suggest what I can do in such case. The matter is in arbitration court. Thanks a lot.