Is it ok to void a part of a contract after both parties have signed?

If you are concerned about the contract you prepared and signed being evidence of the crime of extortion, you should refrain from posting information about it in a public forum. You have the right not to incriminate yourself.

As for your question, you require specific legal advice and should not rely on general information given in response to a question posted on Avvo. You should consult with an attorney to discuss the particulars of your matter and for any specific legal advice.

What you can do will depend upon the value of the 'stuff' that has been broken. If the value is less than $7,500, then you can file a claim with small claims court for the damages your ex caused. Nolo Press has a book called 'Everybody's Guide to Small Claims Court' that will tell you how to file and prepare your case. I have included a link to Nolo Press for your reference.

There are other issues that arise in a Domestic Violence situation that you should seek the advice of an attorney to assist you. The San Francisco Bar Association can refer you to a lawyer who can help you, usually for free or a very modest fee. I include a link to the San Francisco Bar Association for your reference.

Good luck!