Harrassment to collect money not owed

I have been pestered ever since January 11th for a bill I do not owe. Following are dates and events:

11/15/07 - Ordered a free risk-free 30-day trial kit from ONE WORLD LIVE WEB and paid the $7.95 shipping and handling online.

12/17/07 - Cancelled my trial via email within the 30 days of receipt.

01/11/08 - First notice from ONE WORLD received by me. The note stated that prior requests were sent to me for new credit billing information. I did NOT receive any such requests.

01/12/08 - I sent the top portion of the bill received on the 11th along with a copy of my email cancellation and a note explaining that I had cancelled and had not received any other merchandise from them, therefore asked to be removed from their customer list.

01/25/08 - 2nd notice from ONE WORLD received by me. On this same date I called their phone number about the notice and talked to a Jen. This was at 3:50 p.m. PST. She assured me that she would take care of updating my account and give the information to whomever needed to get it.

02/19/08 - 3rd notice received, this time from SKO Brenner American.

02/20/08 - I called SKO Brenner and talked to Shane (or Jane). She said she would notify the company that my account was paid in full.

03/31/08 - 4th notice received, again from SKO Brenner.

04/02/08 - I called SKO Brenner again and talked to Eric. He told me I would have to write a letter to SKO to dispute this billing. So, on the same date I wrote a letter to dispute the bill and asked to be removed from further billings. Unfortunately I had my home phone number on the letterhead and now today - -

4/21/08 - 8:10 a.m. PDT - I received a phone call from SKO (866-281-4135) -- when I denied that I owed anything and that it was explained in the letter, she said "how can that be proof" and I said, "how can it NOT be". She was very rude and threatening.

4/21/08 - Received another notice in afternoon mailed from SKO.

4/22/08 - Mailed a cease & desist letter to SKO via post office with delivery confirmation.