You can use the available slice cash in your account for repaying your outstanding dues.
For example, if you make transactions adding to Rs 5000 in the month of January and get a refund of 500 on one of these transactions on 1st of February, you will get this Rs 500 as slice cash for your repayment in February. Hence, if your total repayment due for the month of February is Rs 3000, then you will have to pay only Rs 2500 and the rest Rs 500 will come from slice cash.
Slice cash gets automatically adjusted in your monthly bill while repayment.