Shortmax Refund and Cancellation Request for Subscription Charge

I have been experiencing a problem with my Shortmax app subscription, which I started and manage via the Shortmax website in the United States. Since around February 15, I have been trying to cancel my subscription through the website, but the system does not allow me to complete the cancellation process. During this period, I have been charged a total of $19.99 for a service I have been trying to cancel. My subscription/payment reference number is S386060622624577. I also contacted Shortmax via email about this issue, but I have not received any response. I request that my Shortmax subscription be cancelled immediately via the website, and that I be provided with a clear written confirmation of the cancellation so that no further charges are made to my account.