petrol instead of diesel. car is faulty no resply

i went to put in diesel after work for a function i had to go to the next day for my work. put in diesel and left. drove to canal walk and back. going there feeling that the car is getting sluggish. later engine management light came on coming home. so the car barely started saturday morning and smoked like crazy. got to work and checked the slip seeing it was petrol the attendant put in. so i phoned them. they couldn't get anyone to fix it over the weekend and i sat without a car. then i had to arrange a tow truck to vw. a rental while my car was in for repair. they did pay me back. but since i got the car back its not been the way it was . they put diagnostic on cleared codes and said i should drive out a tank of diesel so it settles in. on my expense. . i told them if its not in a week im taking it back. also let sasol know. never got any response from them. so im driving my car with no power. engine management light on . i have emailed 4 times with no reply from them. should i take this up with a lawyer? i just want my car fixed and not further inconvenienced.