Any company that you owe or collection agency that is attempting to collect a debt on behalf of a company you owe must collect the debt in accordance with the Fair Debt Collection Practices Act (FDCPA). Per the FDCPA §805(a)(1) it states that "...a debt collector shall assume that the convenient time for communicating with a consumer is after 8 o'clock antimeridian and before 9 o'clock postmeridian, local time at the consumer's location;" In other words, the debt collector can only contact you between these hours.

Please note that this is your local time. I have seen collection agencies try act like it's their local time and not the debtors. In this incident, the collection agency was located in California and was calling someone I know that lives in Louisiana. The call was placed at almost 10 P.M. local time. The collection agency attempted to say that it was still legal because it was not 9 P.M. their time yet. You can read the details of this section in "Communication in connection with debt collection"

You can notify a collection agency that you no longer want to be contacted. This does not get rid of the debt. It only stops the collection agency or company you owe from calling you. Simply send a letter (preferably via certified mail) requesting that they no longer call you. This is in accordance with the FDCPA §805(c).