Why do I have a dent under my eyebrow after Botox that is not going away once the Botox wears off? (Photo)

I got botox in my forehead and what was meant to be a Botox brow lift over a year ago and I noticed straight away that a dent appeared going down from my eyebrow which is more apparent when I raise my eyebrows. I thought it would wear off with the Botox but it hasn't! It also feels like I can't lift the muscle beneath the dent as much as the other side and it kind of pulls the tail of my brow down a bit on that side when I try to lift it..