In 2014, I wrote a post about Copyright Registration Online, one of many faux and exploitative copyright registration "services" that cater to writers' anxiety about theft and plagiarism, particularly of unpublished work, by promising to register US copyright or to provide some sort of copyright verification service.
Naturally, there are fees for these services. At the time I wrote the post, Copyright Registration Online was charging $135--which was a ripoff, on two fronts. You can register copyright yourself online at the US Copyright Office for only $45. Just as important: there's absolutely no need to register copyright for unpublished work.
Some registration services are basically pass-throughs: they do submit registration applications to the US Copyright Office, just at a seriously inflated cost. Others provide their own "registration" documentation or certificates, often based on some sort of timestamp. These might--and I emphasize might--help you prove copyright ownership, along with other materials like drafts and research notes, but there is no legal substitute for registration with the US Copyright Office (in the United States, you must previously have registered your copyright in order to file an infringement action). Just like so-called poor man's copyright, any "registration" received from a source other than the Copyright Office won't qualify.