Faulty Duck

My experience when purchasing a toy duck for my daughters first birthday in September was a pleasant one. The staff were helpful and kind. A few weeks ago the duck proved faulty. The singing duck still moves and make the motion while singing but there is absolutely no sound. When my husband went to see if they could repair the fault they said they'd speak to the area manager as the item is faulty inside. We received a reply a week later saying that we can have a new duck for R150. This made no sense because it's clearly a factory fault as the duck works, just the sound is gone? They said themselves it's an internal fault. We have no idea what the extra R150 would be for as we purchased a working duck for R350. We went on to send the contact at Hamleys Eastgate snapshots of the Hamleys website which says faulty items can be refunded in full or replaced with in one year of purchase? My child's birthday was on 28 September so she's not used it either. We purchased it before her birthday along with her other gifts. We also consulted the consumer act and we are in right standing. I don't understand why they will not give us a replacement duck for our child. We don't want hormones back. We have received no further communication from the store. Please help us. We simply want a new duck?? Regards Geraldine