Store subscriptions are billed in advance, so when a subscription is cancelled, the cancellation takes effect on the first day of the following calendar month. However, the minimum commitment for a Store subscription is one full calendar month plus the balance of the month in which the subscription began, so a seller who cancels during the first month has a commitment through the next month. In other words, your store subscription will end on July 31.
More details here, in the Store terms of service:
http://pages.ebay.com/stores/subscriptionterms.html
If you signed up for an annual commitment, rather than month-to-month, there will also be an early termination penalty fee. All of this is spelled out in the TOS that is shown to sellers when they sign up for a subscription.
