I hardly think that a torrent of emails will overload him.
He can (and possibly does, given the evidence) simply choose not to read them.
If every disgruntled customer were to make reports to their credit-card company, the various trading and advertising standards authorities and to lodge a "Small Claim", that is far more likely to give him something to think about. Don't you think?
Hit him where it hurts him most and where it is most likely to make a difference to his behaviour - in the pocket !
Paul..