Having had, I assume, good experiences with them in the past, I would go in and see the owner and have a rational debate about the condition of the rifle as received and why you sent it back with the action detached from the stock. If he is a reasonable sort, with a mind on future business with you, then I would expect you to get the £24 back.
It is very easy to lose custom over 'misunderstandings' and if he has been in the business for any length of time, I am sure he will take the long view.
Good luck