If you are having problem in getting your t.c from the college where you have backlogs try to contact the authority who are responsible for t.c and migration certificate.

Write a formal letter to the university registrar explaining your situation, stating that you couldn't complete your degree due to backlogs and need a document to prove your 12th grade completion for admission to a new college.

If again it is not helpful then try to Inquire about the possibility of getting a "transfer certificate" or a similar document that verifies your 12th grade completion from the university records from your old school.

Have a great day!!