Cancelled Contract Still ACTIVE

Signed a Cancellation Form for a Data Contract as per their request in store on 3 November 2015. Contract should have ended on 3 December 2015. I received an invoice in January with a due date to be paid on 1 February for a data contract for billing from 3 December 2015 to 31 January 2016?!? Call Centre calls to pitch another contract instead of cancelling or attending to your signed request. HELP as the lines are still Active and still not CANCELLED!!