Kellie,
You are going about this thing all wrong.Stay off the phone!! NEVER speak to any collector on the phone! And, don't be so quick to let someone damage your credit, especially over $15! That is just plain stupid.
FYI...Sprint just sent out a notice about 2 months ago on this third party billing and announced they settled a class action lawsuit and will be paying claimants who were ripped off by this practice.
Forget the BBB. They cannot do anything for you. The BBB has no power to do anything to anyone as they are just a business themselves, not a government agency. You need to communicate in writing, and send only 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. This is very important as it proves what you sent.
Now, with your dispute to the collection agency made, and sent by the means above, you wait for them to violate your FDCPA and FCRA rights, then you sue them for up to $1000 in statutory damages, plus costs and actual losses!
Do not sign any letter you send to a collection agency, just print. In the dispute letter to the collection agency, dispute the amount claimed as not yours. DEMAND to see proof that you authorized it. Also DEMAND that they do not contact you by phone anymore, and that all communications must be in writing.
Hold these jerks accountable. Also file a complaint for the daily harassment at ftc.gov, as it is a violation of federal law to call several times per day, and most state laws are stricter than the federal laws.
Keep in mind that there is no actual enforcement for the individual consumer, and you have to get your own justice.
Have fun with these idiots! Then make them pay YOU!