Worse than that - even if they would take action, you can't possibly orchestrate filing all of the complaints. It's a drown-in-quicksand problem, you can't fight quicksand one grain at a time.
To the ISPs? Each IP range has an abuse email address registered and this is specifically exempt from rate limiting at RIPE's WHOIS server. Not sure how it is in other RIRs but I just happen to know of this policy
You can automate the whole thing, provided that you have a reliable way of identifying the undesired traffic which you need anyway for being able to block it by any means. The trouble is in user identification (they'll just use a new IP address from that ISP or hosting provider if you don't tell the provider about the problematic user)
Others online have been writing about their own experience with the same stuff; it's not unique to PG at all, it's everywhere. Talk to anyone that runs a web server and they'll have these stories...
You also don't have to send out 1k support requests per hour. Could trial it with some hosting provider that you expect is responsive and see how it works out
edit: like, I just don't see another solution short of banning being anonymous online. Each site would have to know who you are. Someone has to be able to track it back to a person that is doing the abuse or there can't be any rules that we can apply. Imo it's better if that's the ISP (or VPN provider, say) who already has this information anyway