Congrats on finding it in within three days. I recently discovered something similar on our infra that had been going on for months (just an INFO log in a tight loop). This is the type of thing that major cloud providers should absolutely have sensible defaults and alerts on, but don't because it's how they make all their money.

It's one thing when it's company cash but I would never ever use a big cloud provider for a personal project (with my credit card). There are way too many ways to accidentally run up an infinite bill. DigitalOcean has plenty of services and more predictable costs, or your local data center will be happy to make a deal on some bare metal servers if you need more horsepower.

I hope you're able to get it reversed - try finding your GCP rep. Either way let this be a valuable lesson on using cloud.