Car Store complaint: Faulty car

Hi made a purchase from Car store borehamwood of an audi tt on 15 April 2019 reg efo7xrw. After 3 weeks from purchase the engine warning light came on.. I thought it was a faulty petrol cap so I decided to watch for a few days.. unfortunately it never went off,brought it back to car store borehamwood as I got 3 months warranty.. on the 14 May 2019 I got a call on the same day say it’s the censor … on the 16 May 20019 I pick it back up as they say it’s sorted.. as I take public transport to work I mainly drive on weekends. Over the weekend the engine warning light came back on. Brought it back on 20 May 2019 store manager say he would have it check out by Audi.. but I receive a call on 21 May 2019 from there service team which she stated that they order another censor which I reply your manager stated that he would have it check out by Audi.. anyway I pick it back up on 22 May 2019. The same issue occurs on the following weekend so I return the car on 28 May 2019.. on my way to return the car while driving on the m25 motor way the car started to loose power luckily I was in the slow lane..now they are telling me they have to do arevaluation on the car. Buy which they sold me a faulty car which by also put my life at risk..