Unhappy with Game service

I bought a laptop online on the 15th June, and the laptop went off the 11th August. Went to Game store in prominade as it has 1year guarantee they tested it and saw it wasn’t working. Nothing was stated online that should it have manufacturing fault, i will have to wait for it to be sent for assessment. I told the managers that i don't want that laptop anymore i wanted to add money to buy another laptop, but they refused to give me the opportunity. I was very disappointed as i needed the laptop urgently, i use it on a daily basis. I’m unhappy with the service the manager was very rude and not explaining to me.