Caller ID not Showing Correctly

Our Company has the Company Name set as the Caller ID under Company info in RingCentral. But even with that one of the members of the Sales team still has there Caller ID show up as UNKNOWN CALLER or as another member of the team when it should just be the company name. This only happens on their Landline phone but not anything else. We have gone into the setting Outbound Calls/Faxes to change the specific Caller ID and it works afterwards temporarily. Then the next day it has changed back to the same problem. Any ideas for a permeant change? Is there something else that could effect it not being permeant like deleting cookies?