How many emails must I send before you cancel this cover!

I took the option of month to month. I was told I can cancel at any point. It is now 3 weeks that I am struggling to cancel this cover. Your reason is I must give 21 days notice! No such thing was told to me, I never signed anything when this cover was taken out that I will give 21 days notice. I have sent the cancellation form back to you completed but not signed. I was not told about ur notice period. I want this cover cancelled . You have taken another premium from my account 17 days after I informed you of my request. Cancel this cover now. I have sent numerous emails and called your pathetic call center and no one can assist. I am 1 email away from getting my lawyers involved!