No one objects to legit third-party debt collecting but people do object to third-party debt collectors breaking the law.

The FDCPA http://www.ftc.gov/bcp/edu/pubs/consumer/credit/cre27.pdf treats the INITIAL CONTACT between collector and debtor (first call, first letter, first whatever) as a special event. Legit collectors per section 809 of the FDCPA *must* tell you at initial contact, or send you paperwork within 5 days of initial contact, the following:
1. $amount of debt,
2. name of the current creditor (which may differ from the original creditor who might have sold your debt),
3. a statement that that debt will be assumed to be valid unless you dispute in writing within 30 days,
4. a statement that that if you do dispute in writing within 30 days, the collector must mail you written verification of the debt,
5. a statement that if you ask the collector in writing within 30 days, the collector must send you the name and address of the original creditor if it's different from the current creditor.
If you don't get the 5 disclosures, orally or in writing (you do not have to ask for them, the FDCPA requires collectors to provide them), treat the collector like you would any SCAMMER.
Note that 3,4,5 must be done *IN WRITING* so you will need to ask an address from your collector. If s/he refuses to give you one for any reason, treat the collector like a SCAMMER.
The collector can threaten court action at initial contact but the FDCPA requires that the collector actually take you to court if the collector threatens it. Threatening court and not going through with it (coercion) is illegal.
If they say the FDCPA does not apply to them because they own your debt, the debt-owner exemption only applies to the original owner. A 3rd party who buys the debt for the purpose of collecting debt is treated as a debt collector and not an owner and must obey the FDCPA as explained in this FTC Staff Opinion letter here http://www.ftc.gov/os/statutes/fdcpa/letters/arbuckle.htm 
You can tape phone calls per your state law described here http://www.fairdebtforconsumers.com/Recording-Laws-Summaries.html 
You can tape, then sue collectors (google "fdcpa attorney") for violations described in sections 805, 806, and 807, per section 813 of the FDCPA.
Has the statute of limitations for your state http://www.fair-debt-collection.com/SOL-by-State.html expired on your debt? If expired, don't pay.
Collectors generally have to be licensed by your state to practise (collect debt) in your state and you can find out by calling your state Attorney Generals Office. Ask if a license is required and does this collector have one. If not licensed, don't pay and file a complaint with your state AG.
Read useful debt-collection FAQs from the FTC here http://www.ftc.gov/bcp/edu/pubs/consumer/credit/cre18.shtm 
The debt collection process explained in plain English http://www.consumeraffairs.com/debt/fdcpa.html 
Be aware that scammers are using bought/hacked/phished loan application data to extort payments for fictitious debts from victims and victims' families and friends.
The FBI warns about payday loan extortion scams here http://www.fbi.gov/news/pressrel/press-releases/paydayloanscam_120710 
The FBI warns again http://www.fbi.gov/news/pressrel/press-releas ... nt-payday-loans 
The BBB has issued several alerts on this scam, just google "bbb.org alert phony debt collector"
Report to the Internet Crime Complaint Center http://www.ic3.gov/complaint/default.aspx , the Federal Communications Commission http://esupport.fcc.gov/complaints.htm , the Federal Trade Commission https://www.ftccomplaintassistant.gov/ and your state AG http://www.naag.org/current-attorneys-general.php as appropriate.