First off, what an idiot! Who doesn't remove them or at least tape before painting?
I wouldn't recommend tackling your paint with a rotary. I would invest in a DA. What type of clay did you use? Meguiars makes an aggressive clay which may work a little better. You could also try using the clay with a cleanse all product. Do a Google search for DP Cleanse All. I sometimes will use old clay with that too remove extremely stubborn stuff as it will deteriorate your clay very fast.
Do you have any pictures? Megs UC by hand probably won't do much of anything except take out very minor imperfections. You could try Megs 105 by hand but again, it probably won't do much and will leave your paint dull compared to finishing it with Megs 205 or another polish.