Slipping and sliding

I love these shoes but they literally won't stay on my feet. The size was correct but when I walk they slide up and down on my heel and cut up the back of my foot. I thought ok, maybe I just need those heel grip things...they made no difference. I tried an inner sole which made the shoes too tight but still no difference! I think it might be the heaviness in the sole of the shoe that just weighs it down. Too bad, because they are really cute