I went through this recently,
Even if you remove SDK connections, if you're still calling
cdn.growthbook.io/api/features/key, even though it returns an error, it's still counted in the billing, to get rid of it, go back to your deployment and simply remove the key, that's the only way to do it.
To avoid this happening in the future, we've used modified version of growthbook-proxy which is routed through a CDN that caches for 30 seconds (which is okay for us) which has dropped the CDN requests by a lot 🙂