I've had a similar experience with idearc (verizon) yellowpages to that described by others here-cancelled advert in yellowpages, they said ok, keep getting bills, then collections call, etc etc.
My opinion is this will happen more and more as they realize their business model is obsolete, and the only way they can make money is to inforce the small print in their contracts, and do all they can to trick consumers into believing they have to continue to pay them.
The good news? Their stock (IAR) is down 99% and trading at 17 cents a share (down from $40). Wall Street already knows their business model is not viable, and there will be no bailout for them. I look forward to seeing them insolvent.
So if you are advertising with them and wisely (in my opinion) wish to stop, you must follow the fine print in the contract you signed with them (remember that from years ago, still have a copy?), and you must follow it to the letter. Notifying them verbally will not work, they will tell you ok on the phone and then continue to bill you and send you to collections/ding your credit if you don't pay them. You must send notice to them in writing to the address in the contract. Send it certified mail and save the receipt so you can prove you sent it when they later bill you and tell you they never received it.
Also, you must cancel at a specified time before the next directory is produced. In my case it was 14 days. This date is not easy to know since idearc wants you to miss it and continue to have to pay for another year.
Finally, if they have already dinged your credit and you feel you have been treated unfairly, why pay them at all? They won't be around much longer and the less money they can raise by misleading consumers (in my opinion) will hasten their demise.
Just my 2 cents