Here are answers to your queries:
1. How to deal this case? Defend
2. Since they didn't mentioned about my certificate whether I have to send a legal notice to relieve my certificate? You can say that in your counter to their claim
3. Can I able to join other company when case is on court ? As i gave resignation? No body can prevent you from joining another company. Go ahead immediately. it is your fundamental right.
4. How long judgement will take? If you appoint a competent advocate, it should take 2 months but moving an application of non maintainabiltiy.
5. Whether the case will be favour to me? Yes, you have a good chance.