Continuing Harassing Phone Calls Regarding Debt

Every month a new collection agency calls about my Verizon account which was closed June 2011.  Since that time, I have paid over $1000 to Verizon which is way over what it should be, and yet I still get calls from a different agency each month.
I have since sent copies of the payments to the credit reporting agencies to see if they have any suggestions about stopping this harassment.