Hello @Barwodder nice to meet you.
From what I can see, Brevo has an Update a Contact module. You can try to use that module, and you can have a List Contacts module and a route where you check if the contact does not exist will be created and on the second route you check if the contact already exists Update the Contact. Maybe this will help.
When you create the contact you can use email as unique identifier and skip SMS field.
If this doesn’t help you please come back with more details and I will try to help you.
Don’t hesitate to contact us if you require further assistance.
//VLAD