Duty draw back urgent pls

dear all,

We have exported the goods under duty draw back, as per schedule of DBK, our product fall into 5 % rate of duty draw back but by mistake we have file 2 % dpk rate in the shipping bill and also that refund already credited to our account.

Is any process or procedure available to take refund of balance 3 % of duty draw back rate against same shipping bill from the custom.

I am on huge trouble pls help me out

regards

sunny