I almost think it's better that he's not giving the flat out no, and that you are showing your difficult child that you are sticking to this, even though you have a choice, because you feel it is best. Just continue to tell him that you love him, but that it's in his best interest for him to earn the priviledge of coming home to see you, then change the subject. You may have to get really tough and tell him that if that is going to be the topic of every call that you aren't going to speak to him on the phone until he can table that subject and change it to something else. Remind him that he needs to focus the energy he's wasting on harssing you about this, into energy spent doing what he needs to do for himself there.
It's not easy, but you saw how your reactions effected him positively last week. Keep that in the back of your mind, how proud you were of yourself and how much good it did all of you.
Hang in there. You can do this!!!!