Legal ways to get back certificates from my college

Respected sir, I am Aravind Raj PR studying in engineering in Kerala affiliated to KTU university. Its a private college.i came from a middile family.I got merit seat in mechanical branch in that college. So I joined there by paying tuition fees of 75000 and caution deposit of 10000 rupees. Coming to the rules,students studying under ktu university must score 35 credits out of 47 credits in order to pass to 3rd semester.I scored 20 credits and was happy because I don't like to study mechanical engineering and this university.So students who fails to score 35 credits are resulted to get year back like which is used in school system.Later strike happened in Kerala to reduce the minimum credit 35 to 26 credits. Finally 5000 students got year back as they don't have 26 credits. So university starts the 3rd semester for the ones who got more than 26 credits.Those who failed including me are got into trap.So we planned to quit the college but they refused to give certificates unless we pay full amount fees for 4years.KTU university then planned for us a special supply for us to join the 3rd semester. But class for 3rd semester already had started.with hesitation we wrote special supply examination.Finally result came and I managed to get just 26 credit. Even though I hate the course and my family don't have money to afford the course ,I joined for the 3rd semester on first week of November 2016.The thing each semester have 6 modules each for each subject.So I must study total of 36 modules in less than 2 weeks as the 3rd semester exam is on December 2 and I joined on first week on November.The class has already completed 5 and half modules and university made me to pay full amount for 3rd semester without any discount as I joined on last weeks of that semester.Now the main problem is that I must score total of 84 credits in order to pass into 5th in order to get that I must pass in 18 subjects this year.6 subjects from last year, 6 subs from 3rd sem(which I didn't attend any class), 6subs from 4th semester.I can't get 85 credits this year and don't like to continue this course,if I do and again results into year back. As a guy from middile family cannot afford this condition and I don't like this course. So we informed them that we are droping out the course.But they are holding my certificates and demanding us to pay full fees in order to get it. We already spend lacs of money here and they are demanding again money. Sir please help. I want to know if there is any legal ways so that I can get my certificates.Even I payed 75000 for 2nd year even though they didn't gave us any classes for 3rd semester.That's cheating,isn't?.. So I want to quit the course as my family is already spend most of their savings in this course.Sir pls reply as is there any legal ways getting back the certificates.. Thankyou