ive been refused a refund for a subcription i thought was cancelled how do i escalate my complaint.

I had a free trial for duo lingo. I believed I had cancelled it before the free trial ended but it obviously didn’t go through. I have been charged the annual fee of £59 which I can’t afford I tried to ask for a refund which was refused and told the decision is final. Not even a pro rata refund. When I complained to duo lingo they advised that Apple would be able to refund my subscription. I’d like to escalate this as an official complaint as I seriously can’t afford £59 right now.