wrong size

I bought underwear at Fourways crossing, asked for help cause I am no longer a size 36C, the lady assisted and eventually I said size 36D fits well, she now assisted to get me the size from the bra I wanted, little did she mention that 36D is finished but she rather gave me 36DD. thinking she gave me the size I asked for cause she was assisting, I paid and left. now I'm stuck with two Bras which are big