Cancelled but still being charged

Back in April I phoned in to cancel my contract and everything was recorded and finalized. To my surprise, they did not debit the cancellation fee in April. Fast forward to June, I'm still being debited the monthly subscription fee and the contract hasn't been cancelled. I have served the notice, and have sent emails following up but nothing has been done. I don't understand why I must continue paying for a service I don't need. Please refund me the money debited after I have cancelled and close the account.