Employer not returning Original educational certificates & salary

Hello Sir, My Name is Alok i am from New Delhi. I want legal assistance on getting back my original certificate and salary which the previous employer holds back. I had joined in a firm on 07.01.2015 and resigned on 30.06.2016. At the time of joining they had provision to sign 5 year contract and submission of original certificate. however after joining they do mentally harass and pay very negligible and treat unethical. i was forced to resign by giving notice period of 15 days and more. however after leaving they are not returning my original certificate neither paid my last month salary. i had visited their office 3 to 4 times they are asking me to pay money. i had filled a complaint on that basis in Punjabi bagh police station and also filled complaint in Labour court in Karampura. however police didn't respond and labour court has been giving only dates. nothing seems to work out. please advice me what should i do to get my original testimonial and salary. Regards Alok