It would appear that you fell for an ad posted by one of those short-lived, Shopify-types of online stores that spring up like weeds as sponsored ads on Facebook and social media, sucker you in with their too good to be true prices on trendy items, then send you substandard junk or nothing at all. Then they close up shop, disappear from the web, reopen under new names with the same goods and scam people all over again.
In most instances, the sites are actually run out of China, which means they are pretty safe when they do this sort of thing. They know you probably won't even be able to find them. Typically, the site is going to be only a few months old and registered for the shortest amount of time that you can register a domain name for, which is one year. Typically also, there will be no address or an insufficient address on the site itself, limited or no contact details and none on the domain registration either.
I'm with you. Facebook should be made to be accountable for the level of fraud on their sites. Presently, they make it clear that they do not vet their members or the offerings posted by any of their members. But once they are on notice about these kinds of shops that are complained about again and again and again and again, it's arguable that they do have some liability for doing more efficient screening and for seeing that fraudulent sites complained about are taken right down.
One day, I expect someone will organize a class action suit against Facebook, but it has not happened yet.
If you paid via PayPal or credit card, meanwhile, you should have some consumer protection. If you don't get what you ordered after 30 days, contact PayPal and open up a claim for an item not received but not as described. You may be able to get your money back.
If you do get swindled, report the fraud to ActionFraud in your country. As Facebook is a US company, report them as well to the FBI online at https://www.ic3.gov/default.aspx which is their Internet Crime Complaint Center, the Federal Trade Commission at http://www.ftc.gov and https://www.econsumer.gov. Also report this to Facebook. It's high time they stopped featuring sites like this.
I'm sorry that you fell for one of these ads and hope I've given you some direction. If you need further information, just reply and tell me what else you wish to know so that you can get all the information you need. I’ll be happy to add to my answer.