Faulty tv

I renewed my contract with Teljoy for a new tv set. The day they came to deliver the set they only put the tv on and we were both happy. Later that night the tv started showing lines all over the screen as if the screen was freezing and duplicating pixels but it went away almost instantly. A week went past and then it happened again also for a very short time. Slowly but surely it happened more frequently. Now it happens every time I switch the tv on and sometimes more than once

Please assist