In your SIP Peer Profile for your SIP trunk group to the Esna, check the settings for Public Calling Party Number Passthrough and Use Original Calling Party Number If Available, also make sure that Trunk Service for that SIP Peer group you have Call Recognition Service set to Trusted.
EDIT: That was my first gut instinct, but I checked the integration guide my thoughts were way off base, the config document is attached, verify your COS and SIP Peer Profile settings match this document... I know it works, have it deployed in an 11 site cluster with no issues.