DEBT COLLECTORS CALLS

One of your Contributors posted 6 items that Debt collectors can not do. One of the items, he said,,,, #6. You can prevent their calls and letters by asking the collection agency to stop contacting you.

Is this True? Must the debt collector stop calling you is you ask them to? I don't think so. They still have the right to call you and pester alleged debtors, I believe. What is the Truth?