Do not follow Foyer's comments. That will land you in even hotter waters as now you're tampering with another person's server, which can violate many different policies.
I've been in this situation before. I'll go ahead and tell you my story, it's kinda long as it's two wrapped into one:
[indent]
When I was just starting out my PHP development, and I was getting good, I decided to help out my summer job which I had worked for 2 years prior, and my local volunteer fire department (to which I am still a member in good standing). Now, for my fire department I agreed that if they paid the server costs, I'd go ahead and do the site for free (since they were non-profit). I started to develop a complete CMS for them. It came with all the bells and whistles like adding photos to articles, repositioning articles, resizing photos, adding photo galleries, adding call information, adding announcements, etc. I also added a "members only" section for those members inside the department and was working to get each member an @myvfd.org email address. And the last part of my plan was to get a digital form of the monthly newsletter together. Anyway, I created one site and it looked pretty good, and worked very well. So they used it without incident and were happy. So as I learned more and more, I developed the site over and over again (probably 3 times in a year) each time with a different GUI; although roughly the same layout. Only once did I really change the layout (between the first and second times). So I went to college, and I had no "middle-man" to proxy information for the site to me. So things slowed down on the site.
As things progressed, I went back for my carnival and the President asked to speak with me. He said the Board was not impressed with my performance and that they were going to hand off most of it to another developer in Pennsylvania. He said I'd still be the lead and I would work in conjunction with the guy in PA. So I said that would be okay with me, and the second developer contacted me not long after that. We started a joint venture.
Two to three weeks later, I got a long email from him stating that he hadn't let down any customer before, and my "lack-luster" attitude wasn't helping and because of me, he was falling behind on the VFD site. So I was cut off from the site and couldn't update anything. So he took my CSS and HTML layout (and images) and dumbed them down to a 3-year-old's level. He "kidded" up the page so that it went for the 5 year old crowd instead of actually giving information out. Today the site still uses the code I created a while ago, but with a terrible set of images (except the header, that was mine).
The other site I was working on for my summer-job was stripped from me because once again they claim I wasn't updating the site enough. Not to mention any of the fact that i had added pictures and kept the member information up to date, and updated the site nightly on the status of the pool (open, closed, temporarily OOS). So they found someone else in the area that provided web services, and she ripped my images from me. So the job asked me what they owed me to finish everything up. So since they weren't giving my images back, I charged them a pretty penny (upwards of $2,000.00). They said it was extortion, and they weren't going to pay, so I removed all my code & images from the site and wrote up a little something for them to say that they would never use my images or layout on the site. They ended up paying me like $800 for everything, and once again, this amateur butchered my code to come up with a piss-poor excuse for a site.[/indent]
So I've had some relatively bad experiences (and yet I still work as a web developer). But each time, I've never really solved them.
If I were you I'd look through all your contracts, and see exactly what is what, and who owns what. I might even get a pro-bono lawyer to help me sort this out. Intellectual property copyright is a sticky subject, and some companies won't go near it, and others get screwed by it. So make sure you know which side you really are on.
If you can in any way prove that the code is yours, take it to the main client, THE COMPANY, and prove it to them. Then tell them to get their money back, and to pay you what you're rightfully owed. You might get their business back too 😉
Just tread lightly. You don't want to burn too many bridges at once, otherwise you'll be on an island with no-one to help you out....