The modal verb “would/wouldn’t” (negative form contraction of would not) is used to refer to typical habitual actions and events in the past. In the given context, the reference is to his girlfriend not being in the habit of listening to him. Thus, “wouldn’t” is the correct answer.
“Isn’t” in option A is a contraction of “is not” and is used in situations that deal with the present. The context refers to a habitual action in past and this option does not concur with the sentence.
“Wasn’t” in option B is a contraction of “was not” and is used to indicate the first person singular (I) and the third person singular (he, she, it), thus this is incorrect in this context.
“Couldn’t” in option C is the contraction of could not and is used to indicate an inability in the present and the future.
Thus, option D is the correct answer.