'PC WORST' shop customer service

newbie so go easy. got a new tower for xmas from said pc chain and it has encountered a faullt were the whole machine freezes.took it back but they would not replace it yet said it was policy to investigate.they offered no replacement machine whilst mine is away or gave a time period.sooo unproffesional attitude all the way through from even the store manager. when travelling costs incurred brought up the cudnt give a pooh. phoned head office and recieved the exact same attitude with no help whatsoever.all because they receipt was over the 28 days, by three days. so im using my old n faithful pc till i hear something from this shower of sh#te. do you think the sale of goods act, goods must be of merchantable quality and fit for purpose. any ideas on my next spet anyone???? with much thanks to any help or support...shyner.