Payment not being cleared by publisher

I worked for a publishing house to write grade 6 maths book. The publisher gave me a contract that stated the following terms: 1.The content writer will submit the complete work on or before 4 July, 2016. 2. The author will add all the features given in the sample chapter. 3. The content will not be copied from any book or google. If it is found or noticed, the publisher will not accept it. 3. Publisher will pay 125 per printed page. This is one time payment. 4. The payment will be released to the author as and when the content is finalised. The author will see the final proofs also before it goes for print. This contract was provided after about two weeks of starting the work by me. The publisher kept adding new features to be added in the chapters. The book was completely delivered to him on the said date. Earlier he promised to clear the payment by end of July. He said the book is in review and it will take more time. Then he said he will clear the payment by 8th august. Then he said he needs to get the book checked for plagiarism. He sent a cheque of Rs 10000 to me which has been cashed. A payment of about 16500 is left. After a few days, he texted me that some questions of about 4 chapters are similar to two of the books he has seen. I have not used any content from any book. I am sure that the work is not plagiarised. I told him to send me scanned copies of the questions that look plagiarised. I told him that coincidentally, if there is anything inappropriate, i will make the changes so that he can go ahead with the publishing. Now, he told me he will need more time. I mailed him saying that just take those questions off that look like they are copied, and clear the rest of the payment. He said he will get it all corrected in his own supervision and will clear my rest of the payment. Now he has started to find more content that looks plagiarised to him. He is not ready to provide me evidence that the content is copied. He knows I do not live in the same city. It is not possible for me to visit his office. I told him to send me scanned copies, which he is refusing to. Now he is threatening me that he will file a legal case against me. I have checked my content for plagiarism on online websites and it is not plagiarised. i am sure of the genuinity of my content. Kindly help me with the matter.