I 100% agree that Pottery Barn Kids is terrible. Williams Sonoma (parent company) used to have top notch customer service and now it seems to be among the worst.
We had the exact same experience and got stonewalled by PBK.
Solution - Call the manufacturer. In the case of our crib (a 6 year old Dana model), it is made by Simmons Juvenile. It should say on your crib exactly who the manufacturer is and should also have the model number. Look for the stickers towards the bottom on the inside. Their website is
http://www.simmonskids.com/consumer_service.cfm. They answered the phone immediately, and could not have been more helpful. Charged me $14 for parts that I needed.
I don't know that I will ever buy a product from PB again, but I certainly would from Simmons.