First of all, FORGET the BBB! Thay CANNOT do anything for you. The BBB is a corrupt and useless organization. They are a FOR PROFIT business, NOT any sort of consumer protection organization.
Second, the FTC does NOT do "individual" enforcement. Your complaints to the FTC will only be archived for possible future use by other governement agencies, and you will get a generic form letter explaining your rights under the FDCPA and FCRA.
To enforce your rights under any FTC rule, you must bring your own action, at your own expense through the court system.
You say you "made an agreement". But I would bet that the "agreement" you made was over the phone, right? If this is the case, you have no agreement.
This is why it is best never to speak with any third party debt collector on the phone. Doing so will never produce positive results for you, and in most cases will make things worse, as you have found out.
When dealing with any third party debt collector, ALWAYS communicate only in writing, and via certified mail, return reciept requested. Be sure to put the certified# in the body of the letter itself, and keep a copy for your records. NEVER sign anything you send to a third party debt collector. Just print.
Before you agreed to pay this third party debt collector, did you make them "validate" the debt? Was it still within the statute of limitations for legal enforcement action?
FYI...Third party debt collectors CANNOT report your payments to the credit bureaus. Therefore, your payments to them mean absolutely nothing in most cases to your credit score. Only the original creditor can report payments to your account. And, if the payments were "post charge off", they will NOT get reported at all.
Knowledge is power.
Educate yourself BEFORE taking any action or making any agreements.