Unregistered gpa

Hi Sir, One of my friend is an accused in NI Act, as my friend is into interior business, he has done one project. On demand of the complainant, my friend has given one security cheque and one promissory note, and the complaiant has collected all the original contract agreements also. As my friend is not aware of the criminal nature of the complainant. After finish of the contract, the complainant has said that he need to more work to be done, for which my friend has invested a huge amount, and the complainant has given commitment and they made and addendum of contract agreement, that is also with the complainant. After work done, the complainant has not paid single np to my friend and he has filed a false case against him. Now the complainant has send the legal notice on his wife name and he has filed the case on his wife name. And in the case, he has filed one unregistered General Power Of Attorney document and he is attending on behalf of his wife. As the matter of fact, his wife knows all the facts and he is not getting his wife into the court. Kindly suggest us, how to cancel that Unregistered GPA and how we need to get his wife into the court as the original complainant. Its kind of urgency. Thanking you Srinivas