According to the news reports this morning... CoinBase has been swamped with thousands and thousands of new users flocking to Bitcoin with the surge in value... Their systems and support are not handling it well apparently
Still, it has been a long time since your transaction confirmed, they should really sort this out. Unfortunately, this is the danger of relying upon third parties for Bitcoin Wallets... you're effectively at their mercy
Log a ticket if you haven't... and/or add to the one you have pointing out that their original response was rubbish, and the transaction has over 1000 confirmations... the delay has NOTHING to do with Bitcoin network congestion... and EVERYTHING to do with CoinBase being useless
NOTE: You might want to word your support requests a bit nicer