Hello
Your husband needs to contact Abbey and tell them they need to "recall" the balance transfer as it was done in error. They prob wont be too keen but it the proper way to do it. Could take a few weeks, best contact HSBC too and advise them a payment (balance transfer) is being recalled so they are aware of the situation.
As regards the fee, if Abbey wont waive it then threaten to cancel the card, say you plan to use it even if you dont.
Hope this helps
Eco