They are most right in the case of that they can't tell you exactly where it's comming from internally.
Their usage is tracked as it comes out of the modem, that's where it ticks, so it doesn't really know what internal source it comes from. Even most 3rd party routers will not do it per ip if they have any form of usage monitoring... You usually have to get into custom firmware and specialty firewalls, etc.
One thing as min short term I would suggest is to swap the modem. This would eliminate the possibility of Mac address cloning.
The hard part with this is to have to check and 100% eliminate that it wasn't internal... Because if it was could happen regardless of carrier.
Their usage is tracked as it comes out of the modem, that's where it ticks, so it doesn't really know what internal source it comes from. Even most 3rd party routers will not do it per ip if they have any form of usage monitoring... You usually have to get into custom firmware and specialty firewalls, etc.
One thing as min short term I would suggest is to swap the modem. This would eliminate the possibility of Mac address cloning.
The hard part with this is to have to check and 100% eliminate that it wasn't internal... Because if it was could happen regardless of carrier.