You can delete your account on Mistify and all of its data from here.
In order to make it transparent and swift, you can log in and then directly initiate the deletion, which will be done immediately.
Note: Please note that the way authentication works for us for Google Sign-in and phone number OTP, you will be signed up here if you do not already have an account. But even after that, you will be able to delete the newly created account.