What should I do to cancel my wrong account?

Because of comcast technical problem, I got another comcast business account.

So, as soon as I figured it out, I called comcast customer service to cancel it.

And they told me this is not active anymore. Also I got a reference number about my request.

But, after that, I received a bill about this account and called several times to make sure if it is cancelled.

And now Billing department keeps calling me for past due about this wrong account several times a day.

What should I do now? I do not want to waste my time anymore.