As I'm reading it, you only have yourself to blame.
ABC sent me two of one figure once. I knew this sort of thing happened because I had read about it on the boards, but never thought it would happen to me. It was a pain, but thems the breaks. Was I going to keep it. Hell no. I wanted one, and I paid for one. I didn't want the other. To keep it would be dishonest. I need ABC to supply me with otherwise hard to get items. They look after me, so I look after them.
I know this isn't exactly what happened to you, but you have to take some responsibility. Responsibilty to correct a mistake. YOU mistakenly sold it on. Had you bought two, you would have paid full price for two. If, as you say, you didn't want the second and sold it for half. You would have accepted the 'half' payment, had you actually bought two to start with. You thought you had paid full price, but were willing to sell it for half. Why not now. Now that you realise what happened. So I would suggest you pay the full price for the second figure.
You should keep tabs on what you pay for, what you pre-order, what has come in, and what hasn't. You should have known that you hadn't paid for the second figure, and you should have realised that something was wrong, and you should have checked and made sure before you went ahead and sold it. So now you find yourself short. Best thing you can do is set things right. Communicate with ABC and explain that you can't pay them back straight away. Suggest to them how you are going to pay them back. Either you do that or forget about buying from them again because you'll likely get blacklisted. You may wish to ignore them and hope they'll go away. You will be dealing with credit card companies, because, even though you may have excuses or say you were double charged, eventually they'll get to the bottom of it. You will be the one to suffer in the long run. The person at the credit card company wont be the one you deal with, as they turn over staff. Thus you will be ground into the dirt, while they remain fresh and on target.
Pay up or pay the consequences.
