I am in credit, the credit is shown. itunes wont let me use my credit and give me my purchases

I have credit in the itunes store.

The credit is shown.

When trying to make a purchase itunes keeps asking for account information, while I am in credit.

All I want is to draw on my credit and get the downloads.

Any advise?

I have read the tutorials to little avail,the tutorials say i can do what I'm trying to do but wont give.

Thanks in anticipation

Regards to all

Spudz