Cancel my plan now

Apparently you can't cancel the plan...i received a rooter that was not working infact it has never worked...i reported and was told to go return at a nearest store because they cant send courier to come fetch it. Now they telling me i can't cancel because my acc is in arrears???? How so??? Can't they see that it has never worked on their system??? Poor service and rude consultant coughing throughout our conversation amd even apologizing for it...