This can be fixed. Just as ETH and BNB use the same addresses (like if you own an ETH address, you also own the same address on BSC blockchain), CRO and ERC20 is also sharing addresses. So even if you sent the CRO on Cronos instead of ETH, it's still the same address - yours (well in this case I guess it's Coinbase address?). There shouldn't be an issue for Coinbase to see that there's CRO on the ERC20 blockchain on your address. Look it up on blockchain explorer, and you should see the assets there.
This is why you want to use addresses that are your own completely, private keys and all.
Creepybits's post in Withdrawals gone rong was marked as the answer