Reluctancy to refund a defective laptop within 14days of purchase

Theres no words to describe this experience, I purchased a laptop from the Cornubia Branch , the consultants were debating amongst themselves Who should get the sale and made Me wait to do the purchase. I have been having issues with the speed of the device I called the store and get told its an entry level laptop even after explaining that an I3 core Asus should be faster than a Celeron. Took it back to the store within 14 days and get told it needs to be assessed otherwise if I want to return it I will be charged 15 % surcharge fees even though I have the packaging , tillslip and the product is in the original condition. Took it to Gateway Incredible connection and a tech assessed it and did an update only for the laptop to be the same, both the tech and assistant manager are aware that this laptop is defective. The laptop keeps getting worse over time, this time the screen goes black when I need to open the browser then it proceeds as normal. I am telling the store manager of HiFi corp that this isnt normal a brand new laptop shouldnt be doing this and it is unsatisfactory , I brought this to their attention more than 3 times yet they are reluctant to refund me for a defective item.