Hint App Refund

I have noticed four unexpected charges of $29.99 each from Hint, which I believe is related to an app subscription I thought I had already cancelled. These charges were taken from my Chase debit card on June 17, July 15, August 12 and September 9. As far as I remember, I cancelled the subscription directly within the app before these repeated charges started, and I did not expect to be billed again after that. I have not found any confirmation email, which makes it difficult for me to understand why the subscription is apparently still active and why these amounts keep being taken. I request that my subscription be immediately cancelled and that the four charges of $29.99 each be refunded to my account, or that I receive a clear written explanation if the company believes a refund is not possible. I expect this issue to be investigated and resolved as soon as possible.