Wow did you ever get it canceled? I am also trying to do the same thing and there is no one to contact. If you know let me know, please.

I have a samsung phone.  I was finally able to find the subscription. 

Go to the GALAXY STORE app. 

Click on 3 buttons on the top right

Click on My Page

Click on Receipts

Then click on Items at the top

Go to Workout Trainer PRO Plus and 

UNSUBSCRIBE.

 

FINALLY, AFTER 4 MONTHS I FIGURED IT OUT!