I want a new tv or refund

Last year November i bought myself a new plasma tv at game vincent park East London in March this year my tv gone blank i send it back to the store they say they will send it for repairs i must wait for 21working days, they send me an sms to come and collect my tv, that's when I decided not to take it back because now its not the same tv i bought remember it gave me problems in a period of 5months so why should I take it home knowing that its a second hand so I humbly asked Mr Dolth for a new one or my refund but he refused and said they cant do that because they managed to fix my tv so they cant give me new tv or refund me. I even ask the Manager Mr Dolth what if i take this tv and after 7months it gives me the same problem? He then rep**** we wont do anything because it will be out of guarantee 💔