To cancel your account, go to SETTINGS > BILLING HUB. At the bottom of the screen, you'll see a link to cancel (highlighted below). Once there, choose what you'd like to cancel and follow the prompts.
When you cancel your account, you will lose all access to your account and any credits you have in your account. Furthermore, your number will be deprovisioned and released.
If you don't see SETTINGS > BILLING HUB, this means you're still on an older, pay-as-you-go account that has not switched over to one of our new subscriptions. Please get in touch with our support team to cancel your account.