I am the co-writer with my producers on songs that were used for a online video game

You're right to be concerned, but I do not have enough facts to answer your questions.

If you did, indeed, co-write the songs, then you should be a co-owner of the copyrights in the songs. Did the producers fraudulently file a copyright registration behind your back to make it appear that they were the only writers?

I don't understand the reference to "they think it was a buyout".

You should find a local attorney ASAP to help you figure out what is happening and protect your rights.

Disclaimer: This post does not constitute legal advice and does not establish an attorney-client relationship.

Are you sure you only signed a grant of rights to use your name and likeness in the game? Is that the only contract involved in all this?

If you actually co-wrote these songs, then you're a co-writer and entitled to co-ownership of the copyrights. That means you could put them on iTunes without needing consent from your co-writers, as long as you account to them for their share.

Who are these producers anyway, and have you asked them if you can see their contracts? If they think this was a buyout, does that mean they're acknowledging that you're a co-writer? And since they think it's a buyout, how do they explain why you got no money?

Did you get songwriting credit on the game and the website? Are you registered as a publisher and songwriter with a performing rights society? Have you checked the copyright and performing rights society databases to see how these songs are registered?

Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.