Why am I being charged after cancelling my ecommerce account?

I have created an account with shopify jus to see what it is & what it is about. I created an account & on t he 12,13th day of my trail I cancelled my account. I then receive an email a few days after saying I was charged 29.99$. Lucky enough it’s not a card I use & there was no funds on there however I’m still trying to get charged & they are going to try again in a few days. I was abit worried after all i cancelled my account the other day so I don’t know why I am being charged & why my account still exists. Can you cancel my account or someone help me as I can’t contact shopify as they don’t have no contact number. I am very unhappy about this situation