Error while doing prepaid rating through diameter gateway

While doing prepaid rating ,after we pass our initiate request ,an active session is created in the ActiveSession Table where impact quantity field value is 50.0 and the after running update and terminate request we are finding that 0.08 free  currency(non currency resource) is deducted only.

But the prepaid product is configured to charges 1 free currency per minute.

Requested Unit -1800 seconds(this is seconds allocated for that session)

Used Units-1200 seconds(actual time used)

The problem is :

1.Same 0.08 amount is deducted every time inspite of changing Requsted Units and Used Units

2.Impacted quantity amount is not getting deducted.