If you haven't already checked, workers, I suggest that you Google your phone number and your working name, maybe copy-paste some text from your advertisements as well. You might just find that you're being "advertised" on websites you have not personally listed with. How can free business be a bad thing? It's not really free business, that's the catch.
There are several websites out there - Skokka is probably the most notorious - who scrape ads from Backpage, Cracker, Eros, and other legitimate advertising platforms, and put them on their page to attract traffic. Sometimes they get the details right, and your number and rates are next to your picture. Sometimes they get them hysterically wrong, and your name is not associated with your images, and your advertisement text describing your "dark olive skin" and "long brown hair" is next to an image of a white woman with short blonde hair - they don't even bother to change the details. Obviously this is one drawback; clients being very confused as to what you look like. But there are more sinister ones.
Imagine Skokka scraped your ad in May 2017. You haven't known this whole time, and in the intervening period, you have changed your rates, changed some services, dyed your hair blue, and lost 5kg. You've had some new photos taken and updated all your active ads to reflect the changes, but Skokka doesn't double check and keep ads up to date. So now you have clients messaging you, angry that you're quoting them $300 for one service when the ad they saw says $250. On top of that, they wanted the brunette curvy worker they saw in the ad, and you could end up rocking up to a booking and bearing the brunt of their anger for not being as you were advertised, not to mention the poor reviews that may happen as a result. It isn't "free advertising" that you should be grateful for if it can legitimately lose you business, get you poor reviews, and put you in danger. And you have no control over that listing. They could change it to say whatever they want. Chew on that one for a hot minute.
What is their motivation then, for advertising you for free? They're not doing this for altruistic reasons, but they're also not out to directly harm you; you're not paying or interacting with them at all. Data mining and advertising money driven by clicks is one reason. Your potential clients are probably having their information collected and sold when they sign up for websites like this, and their clicks on pages filled with sidebar advertising is giving the website owners money - do you feel comfortable with your image being used like that? The slightly less nefarious motivation is usually that they're yet another escort advertising platform that thinks they're going to get a slice of our pie by getting us to pay them to advertise - but to do that, they need to become a popular place for people to go, so they scrape the info of a bunch of escorts off Backpage, and voila, it looks like they have legitimate, paying customers.
In order to stop this, you can try a few things.
1. Contact them and ask them to remove your ad.
2. Issue them a DCMA notice.
3. Issue them a Cease and Desist letter.
4. Find them on a WhoIs database and contact their host to inform them of the theft.
I don't think option one usually works, since most of these guys are really practised and do not care about your nicely worded requests. You can find templates for options two and three by Googling "[DCMA/Cease and Desist copyright infringement] template [your country]"; then it's a matter of replacing the words and sending them an email with a nice legal PDF attached. It might take a while for them to remove your ad after you have sent it, which is why you make sure to include a date they must respond by, confirming they have done as the letter instructed, or you will take further legal action. Option four will really light a fire underneath them though, because hosting companies take intellectual property theft quite seriously - though I haven't resorted to this option just yet myself. I'm yet to come across a website that did not comply with my request, so I've not had to take further action and can't help you past this point, but there are many workers with legal experience who could absolutely give you a hand.
As an interesting note to all this: you may just find when you Google your ad text, that another worker has stolen your copy. A friend of mine found that, and was incensed - obviously this wasn't going to make clients too confused, but it is blatant ripping off of your hard work, and obviously can't be left alone. If you become the victim of this, a few steps can be taken - preferably in this order:
1. Contact them and ask them to change their wording, as it is unethical to plagiarise someone else's work.
2. If they respond rudely, or don't respond at all, report their ad to the platform, and get others to do the same if need be.
3. If this still fails to get it taken down, issue them a Cease and Desist. This probably won't get them to do as you've asked, but it does give you the legal backing to then tell the platform that you've done so, and that you may have to threaten them with the same if the ad is not removed.
Just a quick edit at of this morning, April 6th 2018:
Here's the cease and desist I sent AdultLook.com. The address that's blanked out is actually for SWOP ACT, but I didn't want to put that on my page and have people send the weird stuff. Feel free to use my example exactly! Just change up the relevant details. But note that this is an Australian format! If you would like help with American or Canadian ones, shoot me an email and I'll give you a hand - no charges or anything, just be a sex worker!