The car that was sold to me was not in a good condition

Good day, I bought a 2011 Mercedes Benz A180 in July 2019 with the engine light that was on and Mark said that it will go away after a while. Yesterday a message come on that we need to take the car to a workshop and the car don't have any acceleration. I sold my 2012 Kia Cerato Koup 2.0 to We buy cars to get a smaller car now I must use a taxi to get to work. Please advise what I need to do because Mark said I must get the car to him and then we buy car will check if this is my problem or theirs. This is not customer service. The car I traded in was in a good condition.