There seems to be a lot of this going around lately. Bills, mistakes in billing, and id theft cases that were resolved around the time of various mergers suddenly going into a collection agency (AFNI) after Verizon sold off these bogus debts to AFNI as out of statute, uncollectable debt.
The culprits are AFNI and Verizon it seems. Sad, I will have to switch from my Verizon phone service that I have had for about 8 years over a little more than 30 bucks myself.
I can only tell you what everybody else already knows: dispute the debt if it is not yours or tell them you don't owe any money if you don't owe it, send in a certified letter telling them this and demanding that they validate their claims with proper documentation (billing history, bills, addresses and so on). Also make sure they are licensed to collect in your state, and all that other stuff.
Next, you need to inform the Attorneys General for your state, Illinois, and the State where the problem is happening, your state's Department of Consumer Affairs, and file a complaint with the Federal Trade Comission.