VoIP KX-UT113 connected to a BT home hub 5

Hi all,

My sister has a Panasonic KX-UT113 connected to a BT home hub 5.

She has two providers providing a line each. sipgate & localphone.

The problem is, the phone has been ringing all day and night with phantom calls from number 100.
I have a near identical set up, but i do not use the bt home hub 5 and i do not receive the ghost calls.

Can anyone offer any advise on how to get the phantom calls to stop please.

Many Thanks

FYI

SSAF (SIP Source Address Filter) was enabled in the security options and all the ghost calls have stopped.