Hi,
Check/share current status of CUE:
Command: service-module integrated-Service-Engine 0/0 status
Are you able to login into CUE?
Command: service-module integrated-Service-Engine 0/0 session
The issue with specific series of phone or phone type ?
Please share the diagnostics ran and their output.
Please share the error message with screenshot that you get while connecting to VoiceMail from CCA.
Any recent changes performed which might result into this issue.
You can ping the server from UC or from computer? Please share ping results.
Also, share the "show run" output.