People who are past due on their bills often don't like to answer the phone or check the mail because of collection attempts by debt collectors. While it is understandable that they will try to collect what's due to them, there are limitations to what they are allowed to do. The Fair Debt Collection Practices Act (FDCPA) sets certain standards and limitations for this.
The FDCPA strictly forbids creditor harassment and abuse. They can't call you repetitiously just for the purpose of annoying you. They can't threaten to harm you or do anything violent to you. They can't use profane language or refuse to tell you who they are. They are also forbidden from publishing lists of individuals who refuse to pay them.
When you do speak to a debt collector, they must accurately represent themselves and the situation. They can't claim that they are attorney when they aren't one. They can't make false threats about having you arrested or make any other claims that they can't legally make happen.
It is possible to take legal action against a debt collector who isn't complying with the FDCPA. This can send a stark message to them that you do know your rights. Typically, they will have to pay for your attorney fees and possibly for damages if you win the case.
If you have more debt than you can handle, you do have the option of filing for bankruptcy. The collection attempts stop when you do this because the court issues an automatic stay that forbids them from contacting you. The bankruptcy can also help you to obtain a fresh financial start.