The service team sent back a bunch of general information about costs and instructions to remove a "Metric Filter" which from my follow-up I can confirm does not exist on my account.
The detailed billing shows charges like this across US regions:
$0.00 per request - first 1,000,000 requests 239,785 Requests
$0.01 per 1,000 metrics requested using GetMetricData API - US West (Northern California) 295,570 Metrics
Do others have experience with miscellaneous charges that are impossible to cancel? Any tips for dealing with support on this to get answers beyond copy/paste support articles?