Subscriptions

I have just paid 19.95 for an app ( I thought it was a pay monthly but took the full amount) I tried to use it and it doesn’t do what I wanted it to.

I went to subscriptions and all it would allow me to do was cancel the app, which I did but instead of allowing a refund it has given me access for a year. So how do I get a refund. I used it for less than 2 mins.