Cancellation of cover

I have been trying to cancel platinum life cover of which I feel like I was *******.i made it clear that I can not afford the cover and the guy who called me a thousand times said there is a debicheck and that I needed to authorize the debit order. Well I thought to myself I will just not authorize it. I received an sms from my bank stating that the authorization request expired.to my surprise I received another sms stating that the debit has been authorised.i am really disappointed with myself for believing your agent and giving out my banking details, believing that I will cancel in the 30 days