Paid bill and Comcast sent it to collections [Have Proof]

In April 2015, Comcast sent a bill I paid to a collections agency.  These ridiculous letters from Convergent have been following me since then and I've chosen to ignore it.  Well, this Comcast mess up is the ONLY negative mark on my Credit Report and I want it off.

I have my old client account # for Comcast.  I will need help looking up that old bill that I know I paid.

I have my credit card statement from 2015 for the exact amount that was sent to collections.

Please help me with (A) providing the old bill, (B) informing Convergent that the debt has been settled.

Filing a dispute with the credit bureaus and consumer affairs is next.