SIP INVITE Ghost/Bogus Calls - and Allow Direct IP Call settings

[dbsslc2015]

I am but a lowly user with the tech knowledge of a network admin. We have a small office with three yea link t26 phones on firmware 6.60.72.1. Of three up phones in our office only mine is plagued with these ghost calls. Can you tell me if there are any simple steps that can be taken for me to stop those calls? My VoIP phone service provider told me to blacklist the calls, but there have been so many from so many numbers that my blacklist is full.

Any help would be appreciated.

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That should have said "without the knowledge of a system admin". Sorry