Applicability of Service Tax

if say any financial institution quotes interest to its borrowers in multiple component e.g. say gross interst rate is 18% out of which Normal Interst is 15% and service and tracking interest is 3%. Second type of interest is collected as a additional services provided to the borrower. My query is - calling something a interest cannot not make it a interest if it is collected against the services. My view is that it should be covered under services and service tax should be charged on it. Kindly help