I would suggest it is either an issue with the diversion on your main business number, or within the DID programming as suggested by CoralTech in 22-11.
Do you know if the SIP is still currently registered? You should be able to ascertain this through PuTTy and turning on settings in the 9100
10-20-06 - set port, by default I use 8006
90-31 - Turn on DIM Access over ethernet
Open PuTTy, select Telnet, put in your system IP and Port 8006
Login by default should be SV9100, password 12345678 (Please Note, that when putty first loads, there is a ' in the login name, so I press enter to get another blank username field)
type ip info a
This will show you all the possible SIP Trunks, scroll to the top and it should show if your SIP is registered.
-----------------------------------
IP TRUNK REGISTRATION INFORMATION
-----------------------------------
H.323 TRUNK:
not REGISTERED to GK (SD)
SIP TRUNK:
[RegId0][UserId:******] REGISTERED to SIP Server(9/9 8:25)
[RegId1][UserId:] not REGISTERED to SIP Server(9/8 16:12)
[RegId2][UserId:] not REGISTERED to SIP Server(9/8 16:12)
[RegId3][UserId:] not REGISTERED to SIP Server(9/8 16:12)
[RegId4][UserId:] not REGISTERED to SIP Server(9/8 16:12)
[RegId5][UserId:] not REGISTERED to SIP Server(9/8 16:12)
[RegId6][UserId:] not REGISTERED to SIP Server(9/8 16:12)
[RegId7][UserId:] not REGISTERED to SIP Server(9/8 16:12)
This will tell you if at least your SIP is working and rule out one issue.