How do I go about getting a web designer to release my .TV web site? He used my company name and will not release the domain to me?

I contacted a representative from a website called . TV to design a web site. His charge for setting up the site, adding photos, videos and music to the site was $400. He said he had to secure our company name on the domain and he said since I did not have an account with the .TV service, he would register it under his name and then sign it over to me once it was completed and he was paid in full. We started working on the project on March 15th of 2008. As of this date, I have paid him $300. He has made grammatical errors which I asked him to correct. He stated he would however did not. He had a friend of his check the website and she told him the DBA name was grammatically incorrect. He called to tell me I had a problem with the name and it was going to take him additional time that he had not planned to correct it, indicating he needed more money. I told him that was his error as I told him when I reviewed it, it was wrong. He accused my of disrespecting him and said not only was he not going to finish the site, he was not going to release the domain back to me. He is now claiming I missed appointments which I did not and that he gave me additional time. I have a signed piece of paper with his typed name and signature which states the site was to be turned over to me upon completion. He acknowledged in the first receipt the payment he received of $200. I paid him another $100 on the 24th of March. How do I go about getting my domain released from him