Held hostage by Vox Telecoms

Vox refuses to uninstall their router after I cancelled their account. I cancelled my account in October and am unable to install another service provider until Vox removes theirs. They have switched off the Wifi and have communicated that they haven't booked technicians to uninstall, when I cancelled 2 months ago. Multiple calls and emails have not changed the situation. Vox is punishing me for being unhappy with their service and cancelling.