Online disappointment

I love Zando! However I have been left disappointed with on of their leading brands. Recently I have purchased a Sissy boy twin pack bras that suppose to be Double push up, but there's no push up,just padded, so anyway sincing I can't return the underwear, I have decided to give it a try and wear them, Oh my goodness, I have been having horrible nip slips the whole morning, I normally take a C cup but I upsized to the D cup, because I previously purchased a Sissy boy C and it was small. Their sizing and cups are way to off.