Onecard FD TO UNSECURED PROBLEM

Hi..i recently upgrad offer from onecard from SBM FD CARD TO BOB UNSECURED CARD. So while upgrading it it show i will receive negative outstanding balance of Rs6000(excess paid+point redeem). So on upgrading my fd account closed immediately and new card was issued after 24 hours. They issued only refund of Rs.5400 which was excess paid by me after deducting 600 which was acquired by point redemption. 

Check emails -

Greetings from BOBCARD One Co-branded Credit Card Customer Care!

As per our telephonic conversation you wanted the confirmation regarding the excess amount reversal.

We have checked the details of your account and the repayments which you have made using the reward points cannot be refunded, we have initiated the refund for the rest excess amount that is 5400 apart from 600 (which is repaid through points). 

We regret to inform you that as per the policy we cannot refund back the excess amount which is repaid by points.

We appreciate your patience and understanding in this matter. 

Question- what step can i take to recover amount? They didn't issue any warning of that amount forfeit also they are not reversing the point or also not giving credit in new card.