THREATENING E-MAILS

These people keep on sending E-Mails and threatening to list me on ITC even though I paid the account and sent them proof of the payment. They do not even respond to any of the mails that I am sending them or confirming that they received it. Do they even read the mails? When asking for a Statement of Account, I do not even receive it, but they demand payments!!!! Why should I pay and not know why???