For products purchased online, you get 14 days return window by law under the Consumer Protection Act, this starts from the day of its delivery, not the day of purchase.
So get it touch with them, make sure they understand that its been less than 14 days since the day of delivery, and the product was delivered damaged.
They MUST accept the return, AND reimburse any postage costs involved in returning the item. They can offer a replacement, a credit voucher, or to have it fixed, and you can choose that if you'd like, but you can also chooss to send the item back for a full refund back to your original payment method, regardless of their own policies.
If you have a trouble coming to an agreement, make you sure you get some evidence of your correspondence in writing, such as an email, where you have explained that you are within the 14 day period, and that you want to return the item due it being damaged on arrival.
This is because, once you make contact, that 14 day period pauses, so even if it takes a month to come to an arrangement, or they take too long to respond, you are still covered under the 14 days.