Faulty bike after 2 weeks from Amazon - should they collect it?

[str]

I purchased a kids bike from Amazon and after two weeks the brake mechanism failed (I suspect it's a design flaw) so I contacted Amazon to arrange for their courier to collect it and process a refund also stating a replacement was out of the qestion and I intended to buy a different bike (at twice the cost of the faulty one) because I questioned the build quality of the faulty one.

They responded by sending out a replacement for the original bike but I was too late to cancel it so I refused delivery and contacted them again around 2 weeks ago asking that they collect the faulty bike and I purchased another bike but so far they have not responded.

Is it right for Amazon to demand I return the faulty bike or should they collect it?

[BUFF]

iirc you need to make it available for them to collect but you don't actually have to return it yourself (but I could be wrong).
Best to contact CAB.

[Cybix]

If you told them that you wanted a refund for a faulty bike and they sent another bike out then they are liable for postage and collection as far as I am aware due to the short amount of time involved. If you have any problems I agree that you should contact CAB or get in touch with Trading Standards.