Totally not acceptable! When you 'custom order' something it means just that...it was made custom for you, the way you want it and that's what you paid for...a cake made just the way you wanted.
Was this the color and design that you ordered? Did they take notes when you ordered? Did they give you a receipt with your colors, preferences and instructions on it?
I would return the left over cake and remind the shop of what I ordered in the beginning and demand a full refund.
Oh...and...
to your husband!