Any comments on experiences with Debt Negotiation firms, firms that claim to reduce one's credit card debts?

After a divorce, my debts with credit card companies, especially with new increased minimum payments are unachieveable, and I'm looking for relief - these companies claim that,for a fee, 15% of the negotiated total = typically 50 - 60% of the original balance, they will negotiate with the credit card companies and you pay the lesser amount, something you can afford - are they for real and do they work?