The only way to get the credit according to their support is to pay with PayPal and then contact them with the order ID. They will then manually deduct the amount from the order. I too tried placing an order over a week ago with BTC after they first told me I had a credit and no credit was shown or applied on the order along with no coupon. I contacted their support again and they gave the pay with PayPal and contact them answer others have also received.
well that will be an issue for me - 2 years ago I ordered 10.6k worth of miners from Alibaba seller - who never delivered - I used PayPal, after 3 months with no miners or even a tracking number, I filed a claim, after a month more of going back and forth with PayPal, they refunded the 10.6k order but also promptly closed my payPal account and said I was a "risk" not sure why I got that but I was also happy to get my 10.6k back.
Long story short - I cannot use my corporate PayPal account to pay or place orders any longer as the account has been closed.