Query about college is refusing to give my original documents

I am an engineering student of radhaswami institute of technology jabalpur m.p. I took admission in above stated college in 2014. I have completed my engineering and now college is asking me to pay full fees 92000 after completing my degree and refusing to give my original marksheets and other documents back.they didn't gave any notice before completing my degree regarding any pending fees.i have already paid the amount which was asked during the course as tution fees.now they are asking for more money at the end saying administration forgot to ask for fees before.kindly suggest me what to do to get back my documents.