For anyone who wants to pressure them, their official complaint channel is formalcomplaints@revolut.com.
To be sure it reaches them properly, do it from the email address you registered with them, and put "Formal written complaint" in the email subject.
If they don't reply and agree to support GrapheneOS, look to escalate to your country's financial/banking authorities. They may be able to pressure without requiring a lawsuit.
A few arguments to keep in mind if you reach authorities:
- they don't seem to provide any reply other than "security reasons" (without detailing them even after asking details), and "get a new device"
- there was no announcement or notice
- users who are logged-in on GrapheneOS can still use the app, so this is clearly not about security or about being dependent on a specific Google service