do not pay the tax, did they give you the receipt thingy yet? the tax will go straight in the guys back pocket
if they have call up the airport and keep sucking up to everyone you speak to until someone tells you you are right
if you did not get any slip them the customs guy just got himself a new buggy
if you have know success get in touch with a really anti Israel newspaper eg: ynet, jpost. and get them to make trouble for you