HDFC Bank — Prepayment charges 5.75% for car loan

Address: 133001

I had taken a used car loan of 8 lacs on fortuner in oct 2015 for 36 months. I had paid 18 instalments of 27151.
The principal balance is 4, 40000/- now.
I contacted hdfc bank for pre closure they are asking 5.75% charges. App 25000.
It is a robbery.
I was told that no pre payment charges are applicable.
It is cheating.
What legal action can i take.
They are not ready to give in writing for the charges.
Naresh garg.
Ambala.
[protected].
Mail id:garg. [protected]@gmail.com