Ouch, this is a very bad situation. As a business owner of a SaaS offering myself this sounds like a nightmare (and we are on GCP).
Few months ago (in a different company) I had a very positive experience with GCP. We've unfortunately had a situation where a over-provisioned service account leaked. It has, of course, been used to mine crypto by some malicious actor. We've ramped up a very high six figure bill in just a few hours of this going unnoticed. After reaching out to google, and a months long review process, the bill we've ramped up has been dropped. During the waiting period we have NOT paid any bill for the entire time. Granted: we've been told to not pay by the customer service, until the situation has been sorted out.
What I'm trying to say is: there's good and bad, at every major cloud provider.