How can I stop the calls and letters?

There are many way that you as a consumer can stop these violations. First step is to inform your attorney, (if you used one for your bankruptcy. Bankruptcies can be filed without an attorney.) Your attorney should at no cost or low cost take steps to stop these actions. If you cannot get them stopped then you should consider an adversarial action against the creditor. This is a court action that can be started at no cost to you.