I settled with another company for American Express

In April, I entered into a settlement agreement with American Express through the law offices of Mann Bracken LLP. I agreed to a $5,000 payment in April and two more payments of $338.89. I made these payments and the debt was settled. I have a copy of the agreement which states that after those payment, "You will be released from further obligation in this matter." In July I started getting phone calls from AEGIS Recieveables in Irving, Texas (I don't think the calls came from there the callers could barely speak English, sounded Palistian, or something to that effect) I first mailed a copy of this agreement to them and then last week faxed them a copy. They will not stop calling and are rude and tell me they haven't recieved anything. Today they called 7 times in a row and would not stop calling. I was not home and the friend who answered told them so, but they would not stop. I took the last 2 calls when I got home and told them I had filed a complaint with the Federal Trade Commission (I did last night) and that I did not intend to put up with their harrasement. Apparently American Express is trying to collect more, this company got this in July. So I fault them as well. I entered into a legaly binding agreement with them through their lawyers and fulfilled my side of things. They are still trying to get more out of me and will not. I dare them to take me to court!