[brisance]

Depends on what you mean by "ads". I stopped using FB since April but still use WhatsApp because my contacts use it. In the last 2 weeks, I've been getting email spam notifications to check what these WhatsApp contacts are doing on FB. i.e. FB has been sending me notifications about people who are both on FB and on WhatsApp, and only those with whom I message on WhatsApp on a regular basis. The likelihood of this being entirely coincidental is probably close to 0.

[catdog]

They may not use the content of the message but all its metadata which may even be more valuable, alone because it's easier to process automatically.