Discord Admins: What are the most airtight spam prevention methods?

I run a Discord server.

We recently hit the 'Discovery' page, and all we've had from that is scammers.

Some of them appear to be people, so they can evade detection. For example, had a guy join multiple weeks in a row now, posting his message.

We increased the server rule:

- must have verified phone number to participate.

- regex filters to block keywords (he got around this by changing from posting text to posting images of the same message).

He has been banned and rejoined multiple times under different accounts. I am at a loss and considering ditching Discord entirely, as this is not worth my time.