Usage for account with zero balance in prepaid is successful

Hello Team,

We have two scenarios

case 1:

we are able to do usage for prepaid account whose balance is zero.(please note that credit limit is set as zero only)

case 2:

if a prepaid account has 10rs balance then if we place usage which might cost 20rs. so ideally it should consume 10rs and then indicate zero balance but in our case after consuming 10rs,

a new balance bucket is created for 10rs.

Please let us how the issue can be solved