Loan rejected after appointed bank official guaranteed approval

You can't file a complaint against the agent. He might have given you a verbal guarantee only but not in writing. What I suggest is that you better meet the concerned bank official who sanctions the loans to you. You explain to him the problem and you can also tell him that you have gone ahead as the agent assured you that the loan will be sanctioned.
You may have to convince him and tell him that your father's CIBIL Score is now corrected. Once you tell that he may get convinced and help you. I don't suggest you go for a complaint as it will never serve your purpose and you will lose time.
Meanwhile, you can simultaneously try in another bank also where you have known persons. Some banks will sanction the loans faster. You can try such a bank. Otherwise, visit the website of the bank in which they will give you the procedure to register your grievance and please follow that. You can also approach the consumer court of your area and file the complaint there.

You are in deep trouble because of the false assurance of an agent who promised a smooth process of loan sanction. As already suggested, going after the agent will be a waste of time as you may not be able to prove anything. The best solution is to go for another bank that can disburse loans faster or look for some private financial institution (micro-lending institution) who provide loans faster and with little documentation but at a higher rate of interest.

This will depend upon the urgency. You can alternatively look for means to get the CBIL score of your father corrected as that is possible too in a short span but for that also agents are available who will do the work for consideration.

Non-banking Financial Institutions (NBFCs) can solve your issue as they offer collateral-free loan at a little higher rate than Government banks. Talk directly to bank executives and apprise them of the real situation and they might offer some custom-made solutions. Prefer your home bank with whom or your father had a long banking association.

I am deeply pained to note your problems and going through your submissions, the following are my suggestions to get your education loan approved-
1) Since CBIL score of your father at the present moment is rated as low and hence this needs to be corrected within the shortest span of time through some agent and such agents can be located with your deliberations from the banking authorities and they would work for up gradation of CBIL score with the mutually agreed charges between your father and the concerned agent.
2) You may look for some private banks such as HDFC, ICICI, Axis Bank, Kotak Mahendra for approval of your educational loan on the strength of revised CBIL score of your father. Though the interest rates for their loans would be somewhat higher, they need less papers and approval of the loan would not take that much time.
3) Meeting the same agent promising you to get your loan sanctioned, would not provide you desired result other than wasting your precious time.

Banks are very particular about the authenticity of the documents and other details while granting the loan. So, I would suggest to go through the documents and check if there is some major flaw or mistake or mismatch of name or something of that sort. If it is all right and there is no such mistake then one can think of complaining also. One way is to contact the ombudsman if available in that area for that particular bank. That person can help in the matter as banks listen to their opinions in case of disputes.

There may not be any use in complaints at this stage. That can only affect the chances of any revival of the matter and positivity. But all is not lost also. You may still have and try alternatives.
I think you have approached some new generation private banks that usually outsource certain procedures to agencies. The bank will come in picture directly only towards end and at the time of documentation and disbursing. There will be agent and sub agents too for each type of evaluation and verification.

In your case it seems that the agent/sub-agent or even bank is not satisfied with certain parameters required. Of which the main one is the CIBIL score. Low CIBIL score gives a signal of default risk. However the CIBIL score can be improved by knowing what caused the score low. It may be some default in payment of EMI, credit card bill or using the credit limit to maximum all the time.

I always suggest that one should first approach the bank where one has regular dealings. In the present case you may first have a discussion with the agent or bank how-to remedy the deficiencies and go ahead to get the loan.
You may also simultaneously approach a bank which is near your home or where you have regular dealings (if it is not the one you had already approached). You may be asked to provide some collateral securities to mitigate for the risk they perceive.

Time is a factor now. Banks may not reimburse the expenses beyond one year. Hence speed up the matter and do not provoke nor precipitate matters as you are in need.