talk
If he was the same guy you used for the first 40 hours and he was satisfactory last time around, then I would have a talk with him about your concerns before dropping him out of the blue. Student-instructor relationships are after all relationships and when they get off track a little bit, and they do sometimes, you need to do a how-goes-it check. I think if you were flying only two times a week before and now you up it to four times a week, then he may be unable to accommodate and feels unequal to the task. He may feel you are about to leave anyway and has moved into a defensive mode. Talk to him about it and put all cards on the table. You are the customer here, and you have the right to seek the kind and style of instruction you need. Good luck.