constance calls from 8am until 9pm everyday for a collect

i want to make a formal complaint against QT bills.com because i do not owe. They have call me everyday at least 10 times a day. there is no vaild number to contact them to vertify anything that they claim to have from me.they have threathen to send me to court and as well as suing me for theft.  Please give me some sort of help this has gotten to be harassing and totlly unnecessary.