Gmac financial services
Not giving noc for car whose loan has already paid 4 yrs back

Sir i had owned a car in 2001 under hypotication of gmac finance services and given 46 cheque to them out of them 40 cheques r of 1 bank and 6 of other with time i forgot that i had given 6 cheues of other bank so 2 cheques bounces as soon as i came to know about the same i paid 500 rs penaulty and paid the amount. now since 4 yrs i m asking for noc they r not giving .they r asking for 18000rs extra as interest for delay of payment that is only 2 month at that time . i dont know what to do kindly help me