Find out where the site is being hosted, usually through a WHOIS search, and contact the hosting company's abuse department. Try a web search for a template of a takedown notice appropriate for the jurisdiction. For example, if the site is hosted in the USA you can send the host a standard DMCA takedown notice. Make sure the wording is correct.
You can go to a lawyer for reassurance (and if you can afford one), but for a simple copyright infringement notice sent to a web host, this is not super complicated and you can get it done yourself.
Obviously you are 'burning a bridge' here with the company that interviewed you, and you will never do work for them again, but they are treating you badly and it's OK to get more aggressive in your dealings with them. If they later claim this was a misunderstanding and remove your webpage, go ahead and invoice them at full market rate for the work anyway. They may tell you no but it's worth a try. These are all good skills to have if this happens to you again.
I'm guessing we're talking about a pretty small code test that took you maybe a day tops, in that case it's really not worth putting yourself through the ringer just to prove a point. Yes, they're assholes for doing this, but as many have said before, the best revenge is your own success without them.
* Let it go.
* Keep contacting the founder hoping this is just a misunderstanding.
* Be proactive.
For option 3 you would want to write down timeline and gather all of the evidence (commit logs, website screenshots, communications with the founder). After that you can let him know that he is using your work without permissions, submit a small claim court case, or talk to a lawyer.
Later, if he wants changes you have a few options:
1) Do the work and keep in safe, and send a screen shot.
OR
2) Ask for payment up front, and back pay.
Then collect before giving anything over.
Edit: Call him on the phone, leave a message and be totally honest, "I feel you are dodging my communication to avoid paying me". If he's honest, he will pay up, and even be ashamed and embarrassed. If he's dishonest, you'll get nothing, at least you will know for certain either way.
You can simply Move ON. Lesson learned.
Don't expend any more time/money/energy on these clowns!
It's just a little blip in the Grand Scheme of Things.
Utilize this pain as a call to action.
Focus on stuff you can control. Re-Set your priorities.
Now get in gear.
I also assume you have proof that they either requested this of you or that you have all the raw files used for developing the site that a mere visitor to the site wouldn't have, yes? If so, register that with the copyright office immediately so they cannot do so.
They will probably claim a "misunderstanding" to which you can request that they either produce the paper which you signed granting them the rights to your work (which I assume you didn't sign anything) or the financial record showing that they paid you for it (which they obviously did not do).
The big question is this - did you do this as a project at home as part of the interview? I assume you did since I doubt you would be expected to do it right there on the spot, but I could be wrong. If it was on their computer systems, it becomes much more difficult to lay claim since they own everything done on their computer systems. I assume this was done on your free time at home to go along with a fact to face interview and you submitted the finished product before the in-person interview.
I would advise looking at what small claims options your jurisdiction provides.
ALWAYS protect yourself and your work or, as you can see, you’re worthless.
Assuming it was actually recent (as in a couple of months or less), consider actually registering the copyright on the webpage with the US govt.
If your work ends up enabling a wildly successful funding event, you'll be unable to get much more than the federal filing fee if you sue the company for copyright infringement.
Unless it's a registered copyright, at which point you can take them to the cleaners. I believe it's $200 +/- to register, and there are restrictions which may or may not apply in your particular case.
If it's more than 100 hours work you might think about legal action. Less than 100 hours perhaps pull a face when other people mention the company and tell the story off the record, definitely not recorded. The company's reputation will come back to affect them
On the plus side, you now know that you do not want to work for that company!
As for what you can do about what has already happened, definitely consult a lawyer if you feel it is work perusing. It may be worth taking to small claims.
It might be nice to stop this jagoff from being a jagoff to other people but it's probably not worth the stress.
This is a 'security feature' which you could deploy in future situations. I do not believe this particular implementation would be violation of any laws.
Peter Parker: Spider-Man wasn't trying to attack the city, he was trying to
save it. That's slander.
J. Jonah Jameson: It is not! I resent that! Slander is spoken. In print,
it's libel.