Unpaid seller

Hello to all, I am a proprietor of a small firm. In March, 2016 I sold some goods to a party and was promptly paid in less than 35 days. The second and third sale, to the same party, took place in April 2016, 13th and 14th, respectively, But now the party has NOT paid me since today, i.e. 7th June, 2016. The goods were delivered to him and HAVE BEEN USED by him.He NEVER MADE ANY ATTEMPT to RETURN the goods too. He started cribbing about the quality and asked for some discount on the prices. I even did that, BUT, STILL, to date, He has NOT PAID me the due price. The Invoices were raised promptly and delivered to his office and I have a counter photo copy, duly signed by his accountant. All the transaction was clear and documented. In comparison, he is a big shot, and I am a very new entrant into this business. Both of us have offices in Mumbai, however, the "sale of goods" took place in district Raigad, Maharashtra. Kindly advise on how to take further legal steps, In particular, can I file the case in Mumbai since the defendant is from (resides) Mumbai and has his office also. Regards.