You can cancel Stylus4 subscription yourself by choosing Manage Subsciption in Euphony user interfece or by using this link:

https://audiokernel.com/manage_subscription.php

You need to type in your "voucher code" which indentifies your license and also you need to type in capcha code.

Upon sucessfull entering correct data, you will be redirected  STRIPE service where you will be able to:

1) cancel subscription by choosing "CANCEL PLAN"

2) manage your payment information (eg. change your card info for next payment).