One way to get around this is by using the Limit Subscription feature in WooCommerce Subscriptions. This allows a customer to resubscribe to a service and ensures that each customer account only receives one free trial period to a product.
Enhancer for WooCommerce Subscriptions allows you to set a date when users may begin cancelling their services. This stops users from being able to sign up for trials and cancel without ever paying. We suggest that you clearly explain this condition to your potential customers at the time of sign up.