CELCO has started to harass me with letters and phonecalls after I already paid my debt, I called them and I said that the debt has already been paid, then they sent me a letter in the mail stating " based on your phone call and your promise to pay '', while I have already paid. They still send me mail, even though I called XXXX which confirmed that I no longer have a debt since I paid my debt in full. 
In addition, during my phonecall with them today, she inquired about CELCO 's fees despite my repeated attempts to prove to her that I had paid. I have also informed them that will file a complaint due to the excessive amount of stress I was subject to, despite having paid.