try an old school letter?

Here you will find their address.
http://www.dfs.ny.gov/legal/vcrf_0500/20140828%20-%20VC%20Proposed%20Reg%20Comment%2096%20-%20Coinbase.pdf

They are not a scam, so I think this will all work out. However in the future NEVER leave bitcoin at an exchange for more than a few hours. Until you have EXCLUSIVE CONTROL OF YOUR PRIVATE KEYS you simply do not have any bitcoin.