In my opinion, the shop was undoubtedly taking a shot at you. When you placed that bet, did you check back before gametime to see what their new halftime total was? If they had changed it before gametime, then I would assume they were aware of your bet at that time. 500 on a halftime total is something that a bookmaker will see.
You did the right thing by pulling your balance, the best thing you can ever do is to not complain publically, try to resolve a matter with the book, and if you cannot have a resolution, then VOTE WITH YOUR DOLLARS. Nothing makes more of a statement than showing them that you will not do business with them.
If I were you, I would not yet push the 400 back to them. I would call them, and tell them to reopen your issue with them. Tell them that you felt they stole from you and thats why you decided to pull your money out. I would also be willing to start anew with this shop owner, to put every penny of the 400 back in, plus your entire balance. Ask them to put a note on your account about this issue. And tell them to credit your winnings back. At that point, you will have newfound respect with the shop, and they will have newfound respect for you because you will again be a player and they will again be honorable in your mind.
This is a rare occasion, where YOU ARE RIGHT, and you actually have the leverage that they would be using against you.
If they do not credit your account the full amount of the bet, then I would tell them that they are not getting their 400 dollar error back, tell them to stuff it in their pipe and smoke it, and sleep peacefully knowing that you did nothing wrong.
I normally do not promote this type of decision, and if you had accepted the 25 gift as full settlement, then you would be wrong not to give back the 400. However, it seems to me that you obviosly never aggreed to the 25 settlement, otherwise you would not have pulled your balance.
Best luck to you danny.
-lab