I'm a debt negotiator and have has experience with Mann Bracken. When I deal with them, I get put on hold, transferred, put on hold, transferred, etc.
I finally wind up faxing a Power of Attorney from my client cease and desist on behalf of my client. I also demanded complete particulars of the debt (a complete description of all debits and credits, copies of charge slips, etc.) Chase and other credit card issuers almost never respond.
If the matter goes to an attorney, the attorney will contact you and you'll find the attorney more accommodating than Mann Bracken, but don't be lulled to sleep; the attorney is an adversary. The attorney will ask you to provide a dispute and that's when you, once again, demand a bill of particulars so you can determine if, in fact, the debt is owed. Also, inform the attorney the Mann Bracken did not provide any proof of the debt when you requested them to do so.
I'm not a lawyer, but have extensive practical experience in dealing with credit card companies and their agencies and attorneys. I usually obtain 30-50% settlements and quite often, the settlements can be paid over 3-4 months.
You can do it too, if you stay focused.
Hope this helps,
Bernie