"I told him things, but was he listening?"
Translation:Je lui ai dit des choses, mais écoutait-il ?
The first verb is not used in imperfect. "Je lui ai raconté des choses, mais écoutait-il ?" could be reported if it is not accepted. https://dictionary.reverso.net/french-english/raconter
Actually, I am not sure why you could not be telling a rather long story and then use the imperfect. I guess "some things" didn't take that long to tell. On the other hand, we must have been telling it for long enough to expect him to be listening to it, but was he listening?
The word “disait” would translate to “I was saying” and that would be something very short, so usually you would not be using the imperfect. I suppose something could happen while you were in the middle of saying something and then you could use the imperfect. Example “I was saying his name, when another car hit our car.”
I think if it took a while to tell and you needed the imperfect for something long that I would use "racontait", but I think that they just used the simple past and so expected us to put it in the passé composé.
When you tell someone something, “something” is the direct object and the person is the indirect object. In French “le” is the direct object form and “lui” is the indirect object form for him. So, no, you cannot use “le” and you must use “lui” here.