Ask HN: How to reduce malicious free trial abuse?

I'm starting to get a ton of dedicated malicious spam free trial signups at my fintech startup, these don't appear to be robots so I don't think a CAPTCHA will help. They use the service aggressively during the free trial but don't pay. IP bans won't help either, they seem to come from a large number of IPV6 addresses. Here's what I'm considering:

1. Phone number / SMS verification. 2. Credit card required to start free trial

Any other ideas?