If DPA finds Facebook in breach of GDPR they will be ordered to do it with additional fines for non complying.
Art. 58 GDPR Powers point 2:
> Each supervisory authority shall have all of the following corrective powers:
> (e) to order the controller to communicate a personal data breach to the data subject;
> (f) to impose a temporary or definitive limitation including a ban on processing;
> (i) to impose an administrative fine pursuant to Article 83, in addition to, or instead of measures referred to in this paragraph, depending on the circumstances of each individual case;
If FB still refuse, it will end up in the court.
If the courts agree with DPA, then FB will be ordered by the courts as well.
Courts can choose their way to force companies to comply with their orders.