Be carefull ... the dresses shrink when you wash them

I bought a dress from H&M in East London 3 weeks go. When I wanted to wear the dress a week after I bought it, the dress was dirty (from the shop). So I washed it as the lable said I should. When I wanted to wear it the dress shrun****!!!! Do you wash the material before you make the dresses?

Be careful which dresses you buy there because Mine shrunk after one wash now I can't wear it.

I really need a new dress or store credit. This is really unacceptable!