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: 
This sounds like a process problem and not just the typical behaviour of individual recruiters. The good ones never waste their time calling people with no interest. There are plenty out there who are. 

Call their office and ask for someone higher up than a recruiter (manager, owner, partner, etc.). They obviously have a problem of not updating their databases. There needs to be some mechanism in their operations to prevent calling people who are not interested to the point you have to take such drastic measures. It sounds like they do a terrible job at this if they make any effort at all.

They're going to ask what recruiter called you; don't tell them. Here's another chance to point out the flaw in their systesm. Why can't they lookup who in their company called you? The goal isn't to punish the individual recruiters, but a company that has implemented poor policies and procedures.

I hate it when customer service people don't have the necessary information to do their jobs correctly and not waste my time.
Recruiters are scum of the earth. Here are some ways to get removed:

1. Go on an interview with a company you are not interested in, and be the biggest ass you can be and say the recruiter told you things, basically sully their reputation.
2. Have them change your contact info to a temporary #, which you will then abandon in a few months.
3. Get in touch with their legal team and request to be removed, inform them you are on the do not call registry and you have no relationship with co.
4. Retaliate. Sign up for every online newsletter/spam service you can using recruiters email.