Criminal

If you desire to settle, then withdraw the complaint u/s 257 CRPC.

they are aware that is the reasons they are asking clean chit from you.

1. You can pursue your case and fight to get full amount.
2. You can settle for lower amount and withdraw case.
3. Best option in my opinion is to inform them that you are owed 30Lacs and you have approached court on this matter. You are happy to discuss a settlement and withdraw case but you want the full 30Lacs. 
4. See what they say, they may negotiate and agree to meet at some intermediate number. 

Depending on your strength, you can bargain higher amounts before withdrawal of the case.  If the other company is smart, that letter is not only a No due certificate but also may state that you are not entitled to raise the issue in any court in future or withdraw the cases filed if any.

The decision is yours and when the matter is already in court, your advocate is the person that can advise you and guide you to recover the amount.   These compromises can also be settled with mutual consent through Lok Adalats also, and there can not be further appeals against those parties if the award is recorded by LA.

Yes, you can insist that in order to give the "NO DUE" certificate, the company need to clear all  that is due to you.