Nightmare with my 2016 208 1.0 PureTech

I know nothing about cars so sorry if I sound dumb.

The car has 80,000km, I got it 6 weeks ago and I've barely gotten to drive it.

2 weeks into having it the engine light came on and it went into limp mode, brought it to a mechanic and after plugging it in it said it was the 2nd injector so that got changed. It was fine. 2 weeks later the same thing again, brought it to the garage but this time the light had gone off by the time I got it there so they said nothing was coming up. He said he moved some things around to see if it would make a difference. A week or so later, same again. Brought it back with the light still on and it was coming up the same issue. The mechanic said he noticed oil around a spark plug which can usually mean something deeper in the engine.

We got quoted from the warranty what it would be to take apart the engine for a full diagnostic. It was something like €700-€800 and that it wouldn't be covered by them as it goes under diagnostics and they can only cover up to €75 for the diagnostics.

Brought it back to the garage I bought it from and told them this was not my problem, the car had all these issues before it was sold to me so he can either go about getting it fixed or I want my money back so I can start looking for a new car. He said he would get to the bottom of it and a refund would be the last resort.

I hear from him today and he tells me the same thing, nothing is coming up from plugging the car in, so they can't start taking it apart. That they had been driving it around and it was good to drive. He said when the light comes on that he will come and collect it from my house and they can try again then.

It's been an absolute nightmare. Besides the car going into limp mode, it has been lovely to drive. Doesn't seem to be heavy on petrol, oil seems to be fine. So I can't make sense of it. I'm just sick of having to go back and forth bringing it to a garage and not having a car for days or a week at a time. The first mechanic that looked at it for me thought that in the beginning it could just be something electrical, but thought different when he looked again and saw the oil.

Am I completely fucked or is there any hope for me and keeping this car. I'm afraid that he won't give me my money back before putting me through more months of this back and forth