To fix this issue, install the January 2017 cumulative update 5.0.8308.984 for Lync Server 2013, Front End Server and Edge Server.
This issue occurs because the dial plan isn't recognized by the Exchange Unified Messaging (UM) routing application in the following conditions:
The Front End server pool isn't able to forward the call to Exchange UM in Microsoft Lync Server 2013.
Event error 44005 and 44008 are logged in the Lync Server event log.
There's a connection issue between the Front End server and the domain controller.