avoidance of double taxation (between US and Greece)

This is a bit off-topic for this forum, but I'm having such a hard time trying to solve this problem that I'd thought I ask here anyway!

I'm a US citizen living in the US and freelancing for a Greek company. The Greek company needs a form signed by 'my local tax authority' (which has been written and translated by the Greek Ministry), for avoidance of double taxation.

I've been to my local IRS office and spent countless hours on the phone to them. I've explained over and over again that the form I have (from the Greek govt) is to show a foreign country that I pay taxes to the US government (so they don't deduct 20% of my fee). The IRS won't sign the Greek form, and the only form they've come up with is for a US citizen living overseas, which doesn't pertain to me.

Any other ideas of what I can do to get the IRS to understand what I need? The Greek company won't take copies of my past tax returns because that wouldn't 't show a contract between me and them.

Can't you use a Form 8802? See here: http://www.irs.gov/businesses/small/international/article/0,,id=122559,00.html

I was told that 8802 is only used when the US citizen is living out of the US?

Question 11 says to 'enter the number of certifications needed in the column to the right of each country for which certification is requested'. The person I spoke to at the IRS said that this was only if you were living in the country that you were requesting certification for (meaning I'd only fill this out if I were living in Greece). 

Many thanks in advance for any clarification you can give.

Try the Tax Attache at the London Embassy as I think she is probably in charge of Greece (it may be the Berlin or Paris Attache - I am not sure which is responsible for that part of Europe).