Greetings for the day ahead!!!
If you have duly signed agreement , then you can take the legal recourse. However that will hamper your future relationship with client and you will not be able to do any business with them. So, in my opinion , you should first try to reach at a point which is acceptable to both the parties. If somehow, this can't be achieved then
1. Contact a lawyer and issue a legal notice to your client.
2. If this doesn't yield any result then file the case under relevant sections.