Congrats to REI, but now you know.

That could've been an extremely expensive mistake.
Next time, try a front loader washer with very light detergent. Usually you can find specific detergent for down and synthetic fibers at your outdoor stores. After washing it, run a second rinse on it. You'll want to make sure everything comes out of the fibers.
Then, carefully try to move the sleeping bag into the dryer holding it flat. If your bag has tight baffles, it's alright to put a LITLE vertical strain on it. The idea is that holding it vertical, the down will move to the bottom and not distribute properly.
During drying, use LOW HEAT and make sure you put 2-3 (preferrably 3) tennis balls in the dryer with it. These will bang around and knock the clumps out of the bag and help the down distribute evenly. And you may need to run that dryer through several cycles.
Congrats on getting some help with it though