Help! Phone mailbox says mot in service & caller I

For several months I have not been able to access my mailbox or get caller ID. When dialing *99, i hear the message “The mailbox number you are trying to reach in not in service. Goodbye.”
In addition, every single call that comes into my phone says “Out of Area Private Caller” even though they are in the area and had previously appeared on my phone as contacts. When someone calls my landline it rings and rings indefinitely, they do not receive a message nor voicemail.
Both of these features worked for years and then one day it changed and never worked since. Please advise...