Question: There is a particular recruiting company that continues to contact me. I have been unhappy with their performance in the past and have been clear that I am no longer interested in their services. I have had to inform them of this multiple times.

Whenever they contact me, I inform them that I do not want them to contact me further. They oblige for a few months, and then I get an e-mail or phone call from a different recruiter with the same company. Most recently, I expressed my frustration and insisted that I be completely removed from their database. Today, I received another e-mail from them after months of silence.

Is there any sort of legal grounds I can quote or anything else I can say or do to force them to *actually* remove me from their list of contacts and stop contacting me?

Answer: 
I've been a recruiter for almost 15 years, and hearing stories like this make doing my job much more difficult (gives the impression that ALL recruiters act like this, which they obviously don't). [aroth's note](https://workplace.stackexchange.com/a/3733/168) about not giving recruiters your phone number is one option obviously, but many recruiters will respect your desire for privacy. I almost always use email to contact candidates initially and for 'check-ins' occasionally, and generally only make calls when we need to discuss some specifics (beginning of the relationship requires screening candidates by phone, but once I know you pretty well we can handle most of our interactions via email).

I think in this particular situation, 'outing' the recruiter and company might be something that could get their attention (assuming you have some platform to do so). A recruiter's reputation is incredibly important, mainly because the recruiting industry has such a poor reputation overall that people simply assume you are unethical until you prove otherwise (guilty until proven innocent). I know I would be horrified if a candidate posted my name in a bad light to others in their network. That kind of thing might get their attention. Twitter, LinkedIn, Facebook, user groups or professional organizations could all be places you could at least threaten to go public if they don't discontinue their actions. 

The chances of you suing them or pressing charges that would actually hold them accountable are probably low, and they know that. The only real thing you can threaten is their reputation.
If it's really bad, and yes I know a lot of the big tech recruiters are, you do have a legal option. Find their corporate address either off of their website or from your local Secretary of State's Corporations Office and send them a "Cease and Desist" letter. You can find all sorts of templates online for these letters but essentially you are sending them a formal written notice to be removed from their list and to no longer be contacted by them. You also need to mention that failure to do so will require you to proceed with legal action. Also make sure you get a delivery receipt from the USPS.

Either way you can send a cease and desist letter on your own, often without the help of an attorney. Its much a kin to a warning letter. If they still contact you after 20-30 days of getting the letter thats when you either talk to an attorney or visit small claims court.

It sucks when it comes to this but if you are repeatedly called and "harrassed" this is fully within your legal right to pursue (in the US). Harrassment is a crime, regardless of how it happens.