HELP! Rights to Work Produced Stolen?

Hey guys,

I could use the perspective and insight of web designers who have had a similar experience.
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Here’s some background:**
Company A (for short) has been giving me a handful of freelance projects. I filled out a W2 a few months ago for them, and have received 3 or 4 checks from them in the past not exceeding a total income of $500 prior to this project.
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The scenario:**
I designed, developed, and went some extra miles on a website I was hired on to do. Company A was purely a middle man for myself and Company B, committing to very little contributions in both meetings on work. I finished the site maybe a week ago, and yesterday Company A added “Website Created By: Company A” linked to their site on my work, my baby, Company B’s website.

The solution in progress
I contacted Company A with a very neutral tone suggesting that I should be credited for my work. His reply was that I shouldn’t “be caught up in bylines” and if someone wants a site like this one, then I may get referrals in the future. He was continually passive aggressive and demeaning, then tried to butter me up by saying “You’re a talented guy and easy to work with.”

I’m thinking of making icons for both our sites and suggesting that, but I’m confident he will be steadfast in branding my work his own. Also, he has built an information wall preventing me from connecting to hosting.

Hope this wasn’t too long, thanks for reading. Any insight would be most appreciated. I’m about to strangle this guy! Is there anything I can do?