BTC sent to Coinbase BCH wallet
Coinbase has the private key for the BTC transaction (because it should be the same as the BCH address), but it might require manual intervention on their part to recover the deposit and refund it. Unfortunately, their support is swamped with many other issues this month. If you submitted a support ticket to https://support.coinbase.com/, you might just have to wait a while before they get to it.