Difficult to Cancel – SlideShow Maker with Music Fx Review

I purchased this app to make a slideshow for my class. It was easy to use but I didn’t like only one song could be used and it just repeated. I also don’t like the fact that I’ve not been able to cancel therefor I’m being charged for the app and won’t be using it anymore. Can someone give insight on how to cancel it?
Review by teacherofKkids on SlideShow Maker with Music Fx.