If you'd like to remove the option for users to Cancel and refund their subscriptions via My Account, you have 2 options. The first one is to uncheck this checkbox in the Piano dashboard's Edit Business section:
The second one would be to edit the My Account Library Components template by removing this code:
HTML
<tp-menu-item ng-click="refundPayment(libraryItem)" ng-show="libraryItem.cancelAndRefundEnabled">
<span>
<t context="checkout.platform">Cancel and refund subscription</t>
</span>
</tp-menu-item>
You can adjust the periods for which your users are able to issue a refund also via the settings under Edit Business.