Are you really sure the both addresses are identical ? Did you check that afterwards ?
You might have a copy-clipboard-malware which changes an copied address to the attackers one.

But if you are sure those two addresses are identical, all you can do is contact coinbase and show them your first deposit which got credited (to that specific address).
They should be able to find their mistake and credit you the amount.




Since the checksum is 32 bits, the probability of entering an wrong address that will still decode to a valid one is roughly 1 in 4.3 billion.

Thats rather unprobable. Copy/pasting the wrong address or a clipping malware does seem way more realistic in this case.