It depends on the terms; some brick and mortar and online companies won't issue a refund but a credit (even if you don't plan to do business with them any more). For example, passengers of a ship that has recently sunk received vouchers for their next cruise with the same company (on a different ship though ;).
What if the company give me back the credit(not money) so that I could order again, could it says money back guarantee?
In some cases, it may be a reasonable solution (assuming you have received your order and claim you are not fully satisfied; they have paid the writer and the paper is useless to them because it was written to your specifications). You have the paper and may still use it free of charge.
PS - IF you haven't received the paper at all, you should receive your money back (not a credit).