From their own T&C on the website:
'If a valid warranty claim is made within 14 days of purchase of new Goods we will satisfy in full our liability to you by either replacing the Goods free of charge; or refunding to you the price you paid for the Goods if the exact same item is not in stock.
Where you are dealing as a consumer (within the meaning of the Unfair Contract Terms Act 1977 and Unfair Terms in Consumer Contracts Regulations) your statutory rights are not affected by these Purchase Terms ie. if the Goods are faulty or not what you ordered, in this case please provide a full description of the fault and return the defective item in its original box (if any), and return to Bundles of Joy, The Old Rectory, Main Street, Lowick, Northants NN14 3BH with all receipts, warranties, licences, manual and accessories.'
this might help you, if they don't play ball.
I would email them, not talk on the phone, so you keep everything in writing.
Email saying these goods are not of satisfactory quality and you wish to reject them and return them under the terms of the sale of goods act, and you want them to refund you in full.
(unless you are happy to have a replacement in which case say so - but you're not obliged to).
Then write them the letter from the templates page on consumer direct, and they will probably respond to that.