when a company issues debentures, it takes money from its subscribers and the debtenture stands as a security
this issuance of a debenture is evidence of a debt as per definition of debenture given in the companies act
till the time the debenture is not redeemed, the company is also liable to pay dividends
since the company has defaulted in redeeming the debentures and has also not paid the dividends, this will constitute a commercial dispute under the commercial courts act for which you can file a summary suit in the court in its commercial division under order 37 of CPC
Another option would be to file an application under IBC against this company
since its a public limited company, there would be provision for issuing a pre suit notice to the company
also now it is compulsory that before one files a commercial case, he has to first apply to the competent authority under the commercial courts act for mediation between the lender and defaulter company