hi,

see you did not mention which certificates you have not taken from college. well if its the b.tech semester mark sheet you may contact with the university  under which the university is affiliated. you should bring the matter to the university exam authority. once the exam is completed and results has published , if you have cleared your payment for the said semesters then college should not hold back your certificate. legally you can claim your certificates for semester which you have paid the tuition fees and passed in the exam.

another thing I want to mention that  your two year incomplete b.tech semester certificate would not help you to secure a job. every time you will be asked for final marksheet/ provisional certificate.

I suggest you to once again contact with university officials and request to solve the issue.