Is it always the same IP? Unfortunately with VoIP, you do not necessarily need a phone number. You could try to call your provider (lingo) and find out if they can tell you more but just based on the IP, there is only so much you can find out.
Here is the Info associated with that IP:
Search results for: 209.244.23.211
OrgName: Level 3 Communications, Inc.
OrgID: LVLT
Address: 1025 Eldorado Blvd.
City: Broomfield
StateProv: CO
PostalCode: 80021
Country: US
NetRange: 209.244.0.0 - 209.247.255.255
CIDR: 209.244.0.0/14
NetName: LEVEL3-CIDR
NetHandle: NET-209-244-0-0-1
Parent: NET-209-0-0-0-0
NetType: Direct Allocation
NameServer: NS1.LEVEL3.NET
NameServer: NS2.LEVEL3.NET
Comment: ADDRESSES WITHIN THIS BLOCK ARE NON-PORTABLE
RegDate: 1998-05-22
Updated: 2001-05-30
RTechHandle: LC-ORG-ARIN
RTechName: level Communications
RTechPhone: +1-877-453-8353
RTechEmail:
ipaddressing@level3.com
OrgAbuseHandle: APL8-ARIN
OrgAbuseName: Abuse POC LVLT
OrgAbusePhone: +1-877-453-8353
OrgAbuseEmail:
abuse@level3.com
OrgTechHandle: ARINC4-ARIN
OrgTechName: ARIN Contact
OrgTechPhone: +1-800-436-8489
OrgTechEmail:
arin-contact@genuity.com
OrgTechHandle: TPL1-ARIN
OrgTechName: Tech POC LVLT
OrgTechPhone: +1-877-453-8353
OrgTechEmail:
ipaddressing@level3.com
Level 3 is a huge network provider here in the US. We use them for our 50mb connection at work. Its possible that someone is assigned that IP or its also possible that someone is hiding behind that IP. If lingo can't help, you could file a complaint with level3 and see what they can tell you (or call their help line).