Why am I being charged for a free trial of Hulu?

I signed up for a free trial of Hulu on February 8, 2018. My free trial isn’t over until March 8, 2018. I can't download anything in my App Store without it saying “there’s a billing problem with a previous purchase” and so on. I need those charges cancelled because my free trial wasn’t and still isn’t over before they tried billing me.