Landmark Ltd. (landmarkonthenet.com) — Placed order, payment has been cleared, but product not received

I placed an order on the website 'landmarkonthenet.com' to purchase a book. I chose for paying by cheque and I sent the cheque of the required amount to the address given on the website. Courier company says that the cheque has been delivered and my bank account states that the cheque has already been cleared on 30th Dec '11. But still the company where I placed my order shows me that they have not received the payment yet and I've not received the product.

S. Koley
West Bengal