First thing to realize is you should not waste breath on these collections nitwits. Verbal sparring does not work. Print does, for the Fair Debt Collections Practices Act (FDCPA) compels them to obey written requests.
Draft a boilerplate letter stating your name and the number they have called to reach you. State clearly that you are not the party they seek, and you are not connected with that person financially, personally, or otherwise. Then request that you never again be contacted by the collector. There, you've just written your new best friend the "cease-comm" letter. Stow it on your hard drive or print a stack of copies, and whenever a new collection agent (C.A.) comes with the same old inquiries about this alleged deadbeat, obtain a mailing address and fire off a letter.
Even better if you can send your notice on a letterhead from your office, clearly showing the phone number the C.A. has been pelting. If you have a website with a contact page listing the same number, refer them there as well. Make it plain they are calling a place of business and your boss doesn't like it. (That fact alone gives you a little extra clout under FDCPA.) Beat it into their skulls until they get it. Collectors are paid on commission and bad ones are not hired for their patience or intelligence.
You must send this USPS Certified with Receipt Request. The C.A. must mark and return the (usually) pale green postcard back to you as proof they have your letter. This costs a few bucks each time but can save you a world of grief later. After that receipt date, the very next contact from that C.A. is your invitation to string them up on Federal charges. You can also pursue them if they try to harass you into paying or apply that mystery person's debt to your records.
Sadly you may have to watch closely this time for just those violations. Allied has attracted a complaint list a mile long for abusive practices and extortion tactics. See these items for a very few of the many irate voices:
If you have an afternoon to kill, drop the phrase "Allied Interstate" into the [redacted] search field:
If you've been fighting this since 2004, the person they want has done a fair job evading the skip tracers, in part by diverting the badgering calls to you. It sounds very likely the same debt has been resold to numerous collectors as each in turn gave up trying. They are supposed to validate a debt before continuing the Hot Potato game, but many won't bother. You may be answering this over and again until the applicable Statute of Limitations expires. Do some homework on the agents who have contacted you and see if they are DBAs or subsidiaries of a larger firm, then take your complaint right to the queen's nest.
Luck be with you!