Well technically Google still exists; it’s a subsidiary of Alphabet, and people who work at Google are employed by “Google LLC” (and not Alphabet). (In fact I think I remember there was some training that explicitly told us to NOT say that we were employees of Alphabet.)

The company “Facebook” no longer exists, though.

Yup they rebranded for different reasons.

Therefore to frustrate the marketing efforts of both you should call them Facebook and Alphabet (even when actually referring to the current Google).