Hello I Have Been Doing Everything To Get Rid Of

hello I have been doing everything to get rid of my dark neck . I feel so embarrassed because it has gotten worst and now people started to point it out. I wash my self constantly and and daily but it doest seem to be working and not just long ago I started noticing it in between my breast I fell horrible my mother says its just dirt but why doesn't it go away? please help me recommend me some treatments please.