Precision 7780, 5 months old, damage to power supply

I recently brought a Dell Precision 7780 but noticed the power cable outer sheath has split from the plug. I have only had the laptop for 5-6 months. When I requested a replacement I was told by Dell Customer eupport it was damage and I would have to pay for a new one. It is blatantly obvious to me that it is a manufacturing weakness / fault. I have emailed two of our Dell contacts about this and I have heard nothing. Is there anything I can do as I personally think this shocking service?