Rows at different angles, light shrugs leaning slightly forward (pulling your shoulder blades back as opposed to *up*) and deadlift.. with a lighter weight, so you can really squeeze the area.
It sounds like you don’t have much of a mind muscle connection. Its all about feel. Lighten up learn to properly contact those target muscles and feel them working. I have another really good exercise that nails that area specifically, really well. I just started doing it. But I do not feel like typing that much out.