GDPR Legitimate Interest Clause
@Stratman "I have never had a Facebook account, do not have one now and can't foresee me ever having one, so if they do hold data on me I wonder from where they received consent?"
Other companies that you may have an account with contract out work to Facebook, handing over customer personal information. Under GDPR, they can now justify this under a clause called "Legitimate Interest". This doesn't seem to be widely known about, so it's worth having a read up about it.
I've seen marketing and product development used as a "Legitimate Interest" under GDPR to justify handing over customer information to Facebook, unauthorized. To be clear, this covers Facebook combining the data with the data they already have.