Automatic_credit_control

Hi, Experts,

I have an a issue with credit management,

Currently using dynamic credit check,

The requirment is ,

System shoul not consider open sales orders at SO level for smoe customers ,it will check only for current SO value ,total recivables and total credit limit,if the SO values is >than total credit limit ,system sud block that SO for delivery,

The above one is working fine by using user exit up to the checking part but system is not able to react as per the reaction i maintained like C or D and even it is not blocking also as per the Status/block check box,

Pls guide me how to actve these above two fields for my user exit,

Or provide any other easy solotion.

Thanks in Advance,