Maximum interest charged by a NBFC

Mr. ABC Ltd (drawer) has supplied materials to MNC Ltd ( Drawee) by signing hundies. Drawer discounts the bills with a NBFC Pvt Ltd company registered in Delhi. The NBFC company has sanctioned limits to ABC ltd and calls MNC ltd as a joint borrower. The rate of interest stated in the sanction letter is 22% p a and in case of default 36% p a compounded monthly. Both ABC ltd and MNC ltd have signed the sanctioned letter addressed to ABC Ltd. ABC ltd discounted bills with NBFC company, but defaults in making the payment. The said amount is due to NBFC since 2005. The NBFC company claims the principal and interest @ 36% compounded monthly, an exorbitant sum, which is 150 times more than the principal amount. In the year 2010, the high court orders liquidation of ABC ltd on account of default to another unsecured creditor. Now my questions are: 1. What is the maximum rate of interest that can be charged by a NBFC registered in Delhi, as per the statutes? 2. is MNC Ltd is liable to pay to NBFC company being a joint borrower and signed the sanctioned letter? 3.Since ABC ltd is in liquidation, should the rate of interest applicable to a company which is in liquation as per company court rules or as per sanction letter? 4. Can the interest be more than the principal or is there any restrictions on the same, especially when the interest is more than 150 times of the principal? 5. What is the maximum rate of interest permitted to charge by a NBFC by RBI, Delhi Govt and by union Govt directives? 6. Any other way or releief avaialble to MNC ltd to resolve the issue legally, other than mutual settlement? Kindly share your legal / expert opinion.