Forget about calling anyone! Phone calls DO NOT protect your rights under the law.
ALL disputes MUST be in writing. You really need to send disputes to both the credit bureau AND the "creditor"/collector.
DO NOT sign anything you send the collector, as your signature could end up on a "contract". This fraud is very common in the collections industry.
These disputes need to be sent via CERTIFIED MAIL / RETURN RECIEPT REQUESTED and be sure to put the certified mailing # on the top of the letter itself and keep a copy for your records. This proves exactly what you sent, just in case you need to go to court.
In your dispute be very concise, and to the point. Reason for dispute: "Not My Account". Then DEMAND to see something like a contract with your signature, and an itemized "account" history.
Also, go to FTC.gov and file a complaint for statistical purposes.
STAY OFF THE PHONE!!!! NEVER speak to ANY third party debt collector on the phone!! Doing so can ONLY hurt you.