I have had success by cutting the ivy down hard and then waiting for the new shoots before treating. I used full strength glyphosate on a dry day and then I left it alone. I have found that if you cut the leaves off when it looks dead then that saves the roots and it shoots again, if you get impatient and re treat, that burns the leaves and again saves the root to grow again. It may take a whole growing season to see a result. If you do get regrowth the following year then do it again but persevere and you will succeed.