[Resolved]  Street Style Store — credit slip not working during checkout

I have a credit slip from my past order return (Reference no : ylpohgkwa).
But when i am applying the credit slip deduction with my current purchase, it gets applied. But when i go to the last payment page, it asks me to pay for the full amount.
I wanted a full refund and i was promised one in my last order but was given this credit slip which now doesnt work!!
Can you please look into this asap.