Comment by immibis

Should be easy enough to create a DroneBL for residential proxy services. Since you work on residential proxy detection at a FAANG service, why haven't you done it yet?

If they're doing things the above-board way from their own ASN, block their ASN.

If they're doing things the above-board way from third-party hosting providers, send abuse reports. Late last year there was a commotion because someone was sending single spoofed SSH SYN packets, from the addresses of Tor nodes, to organizations with extremely sensitive security policies. Many people with Tor nodes got threats of being banned from their hosting provider, over a single packet they didn't even send. They're definitely going to ban people who are doing actual DDoSes from their servers.

DDoS is also a federal crime, so if you and they are in the USA, you might consider trying to get them put in prison.