One of the most immediate forms of relief offered by filing for bankruptcy is the Automatic Bankruptcy Stay order. This immediately puts an end to creditors' reclamations, as well as any attempts to seize your property or assets.
This means that all types of creditor harassment, including letters and phone calls, have to stop by virtue of the automatic stay. The stay acts like a court injunction that prevents any creditors from taking any type of action against you or your property. For instance, the Automatic Stay will stop the repossession of your vehicle or the foreclosure of your home.
In addition, if you have a bankruptcy attorney (which you really should) you can have all future communication from creditors go through them. No more contact of any kind will be required with your creditors.