cancelled my line and still being billed

I cancelled my line and account effective 28 Feb 2015. Line went dead on 26 Feb. I have since then received an invoice every Month to date. Can't get through to anyone at customer care. No one responds on FB posts or calls or emails as I've requested. Tried to call and sat on line for 3 hours trying to get to talk to someone to sort out issues but not been able to speak to a human since February! Ridiculous! !