Thanks for coming back to us @chriskan.
Are you possibly able to perform a reset on the hub 3 to return the hub into router mode and then re-setup the modem mode connection to see if this again disables the landline services?
You should still be able to use the landline services whilst in modem mode without any issue.
Please follow this link on guidance on how to reset and place in modem mode.
Kindest regards,
David_Bn