Cant cancel a subscription

Hi!

I want to ask for your help ASAP! Here is my story...:

Few weeks ago I downloaded a free app from the appstore. I had to subscribe in order to use the app but there was a free one week trial, so I decided to try it. After the free trial came to its end, the app want from me 5.49... Every week. I could not find out what is it becouse I deleted the app after the free trial. So I figured it out, it was this app. The problem is, I can not cancel my subscription. If I go to my apple ID and "iTunes and App Store" then my apple ID "view Apple ID" then "Subscriptions" I can see the app which is causing the problem. I can see the possible subscribtions too. The only thing I cant find is the "cancel subscription". Ive tried to do it on my iPhone. And in iTunes on computer too but still the same problem. I just dont have a cancel button. Ive tried to go to Accessibility-Increase Contrast and turn off everything but it do not helped. So I went to the appstore and wanted to download the app which is causing the problem and turn off the subscription inside this app. When I tried to do so, I could not download the app becouse of the error "There is a billing problem with a previous purchase. Please edit your billing info to correct the problem." The billing info is correct but I dont have money on my account. So I cant download the app and can not disable the subscription in any way... Please help I have already tried everything but nothing helped. Thank you for your answer!