The amount a debt collector can charge is no more than that provided in the original contract with the original lender, unless your state law provides differently.
If something smells fishy, trust your instincts. You may not owe anything at all. Your credit report is not a reliable source of all your debts and does not guarantee that you do or do not owe money.
In my state, there is an agency that regulates & licenses collectors. You may want to check to see if your state has a similar agency, and if so, whether this creditor is licensed to do business in your state.
Dispute the debt in writing. Send the letter certified, return receipt requested. Then, consult with a local attorney about possible Fair Debt Collection Practices Act issues.
[I am a Virginia-licensed attorney. This communication is intended as general information and not specific legal advice, and this communication does not create an attorney-client relationship.]