i think TS refer to semi-flexi.. and yes
if you just pay more, its consider advance payment, means u pay for the next half month (installment 1k, pay 1.5k)
means next month you only need to pay 500

or you can do it every single month, but its very inconvenience for you
just go to counter and said paid to principal, and sign a form..

or you can go around half years or 1 years