How do I fight a bad appraisal?

i need some advice. i am trying to refinance my home and i determined that my home should be worth $600,000 to $620,000 based on both zillow and the most recent sales within my immediate neighborhood. i was hoping to get at least $600,000 for the value because i was going to pay the remaining balance down to $480,000. i can pay a little more, but not an extra $72,000! i noticed that the appraiser listed six comps. five were adjusted to account for differences in features, number of rooms, square footage, etc. and ranged in value between $510,400 and $563,845. one was not adjusted at all even though it was 78 sq ft smaller (should have been adjusted up $4290 based on$55/sq ft that the appraiser used to adjust the other comps). it sold for only $510,000. now, can anyone explain how my house appraised at the same exact value of the very lowest comp? i challenged the appraisal on the basis that only the lowest comp was used and that other, closer comps should have been used. the two closest comps were both 0.08 mi. from my house and had adjusted comp values of $563,845 and $544,075 (the two highest because we live in one of the nicest neighborhoods in the area). the other four were all 0.47 mi. or further from our home and had adjusted comp values between $510,000 and $524,575. given all of this information and more (including half a dozen other potential comps worth considerably more than $510,000) the appraiser refused to change his appraisal or consider any other closer comps. he supposedly factored in all of the comps to differing degrees based on which ones he thought were most like our home, but since our house appraised not one penny above the lowest valued comp, this is, by definition, a lie! i feel like i have been defrauded and that the appraiser either made a major mistake which he is refusing to correct even after it was brought to his attention or he is trying to justify the lowest possible value in my home and hoping that i'm too stupid to realize that i've been had. how do i go about getting this corrected? should i contact american appraisal group (they hired this guy), should i contact the appraiser directly, or is there some sort of watchdog agency that i can appeal to so that someone can correct this blatant incompetency? i guess the other options would be to try to have the credit card company reverse the charge or sue the appraiser for incompetence or malicious intent. i have other problems with how the appraisal was done, but i think this post is long enough.
thanks, josh