Billed for OnDemandStreamHr in Kinesis despite no instances running

I've been billed about $30/month for Kinesis "OnDemandStreamHr" at about 720hr/month (so running 24hrs) for the last few months. I was playing around with Kinesis in January when studying for the ML cert, which is when the billing started, so that tracks, but I was very careful to shut down all my instances. I still don't see any running kinesis instances despite the billing continuing to happen. Any insight would be much appreciated.