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.
First step - Check the recruitment companies privacy and/or communication policy.

Second step - For most Western Countries, there will be a Privacy Commissionaire who you can report them too (just make sure you have documented proof that you have requested them to remove your personal details/information from their records)

Third step - Search out and contact the Association body for recruitment/staffing firms (NAPS, ACSESS, REC, etc... and Better Business Bureau).

Fourth step - Draw up a 'Cease and Desist Letter' - would strongly recommend using legal guidance (it might cost but if you feel this strong then it shows you are serious). Each state/prov/country has rules, terms, conditions, and you want to make sure you include terms such as 'breach or privacy', 'harassment' and 'feeling threatened' and 'mental duress'.

Additionally, if you are connected to anyone from that company on social media sites - communicate your intention and desire to be removed from their system, and go as far as disconnecting from them, un-following them, and blocking them.