I'd do a chat with VZW on the main website. This maybe something they need to resolve on their end.
I want to ensure you are able to receive all of your voice mail messages on your iPhone 6 device.
Can you confirm if the actual messages are deleted from the system by dialing *86 then Send? Did your device have a data connection (cellular 3G or 4G/LTE, or WiFi) at the time you deleted the voice mail messages? Also try soft resetting the device by following these steps: http://vz.to/1Od8EGs (Restart your iPhone). Please keep me posted.
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