Possible reasons I know, but low chances of happening:
- fake coinbase wallet, though I'm sure there'd be a lot of reports by now if there's a new phishing scam using coinbase.
- error in copying, yes this happens, this may occur on both copying and pasting, that's why it's recommended to check at least the 1st and last 4 characters of the address. It's ok to be paranoid when it comes to addresses.
Again these have low chances of happening. So if everything you did were correct, coinbase is the only one who can help you since the transaction is already confirmed. I'm not sure if the customer service hotline would help but give it a try. Then again, coinbase is known for shit customer service.