jeweler broke my diamond

I noticed right away that the setting in my engagement ring was lopsided and there was a small (sliver) chip in the corner of the diamond (1.22 princess cut) We showed the certificate and the diamond to several other jewelers who all said it was without a doubt from the (benchman)setter. We returned to the jeweler where it was purchased & set and they said that it was impossible to set a diamond evenly (even the prongs were mismatched) and that the chipped corner was not the setters fault (they said possibly it got weak from being set and broke after wards). What options do we have??