We can't cancel accounts that have active domains in them, though you do have a couple of options.
If you plan to keep your domain(s), you can transfer them to another registrar, then we can cancel the account once that's completed and the account us empty. Let us know if you need assistance initiating that.
Alternatively, you can set the domain to expire and be deleted from your account, and once that's done we can cancel the account.
To turn off the auto-renewal for the domain, login to your iwantmyname account.
Go to this page and click the red Quit renewing this domain button:
https://iwantmyname.com/dashboard/domains/expire/<< domain.tld >>
Your domain will now expire at the end of its current billing cycle and then will be deleted. Once that's done, let us know and we can set a flag to cancel the account once the domain is deleted from our system.