How do I cancel Marco Polo Stay in Touch?

Contact iTunes Support for assistance. See the Apple Support articles below for contact information.   

iTunes Support – world wide 

Apple Support schedule phone call     

Billings and Subscriptions 

If necessary, try Twitter

https://twitter.com/AppleSupport.         

If the subscription has an Expiration date, there won't be a cancel button. When the subscription expires, it is not automatically renewed.