How exactly am I supposed to know that Acxiom might have my data if I don’t even know that they exist? Like, I know Google and Facebook does and I know where to

How exactly am I supposed to know that Acxiom might have my data if I don’t even know that they exist? Like, I know Google and Facebook does and I know where to find it but Acxiom doesn’t even have a page when I can ask for it.