Verizon - Verizon Wireless Collection letter for $21.05 for charges allegedly incurred over two years ago Internet

I received a collection letter from I.C. System in the amount of $21.05. That peed me off, I've never received a dunning letter before, least of all for such piddling amount. The missive does not detail what the charges are; it merely advises me to write a check in the name of I.C. System for that amount or, of course, additional charges will pile up, blah blah. I keep detailed accounts on all my payments: I took out a two-year contract with Verizon in July 14, 2004, the contract expired two years later and I still kept their service going for an additional year, without a contract. I was notified by e-mail when payments were due and I equally made e-mail payments. I contracted with Sprint in August 2007. Anyhow, I paid my last bill with Verizon, $48.31, on July 26, 2007. I  notified Verizon of my termination of services. No further word from Verizon on the matter, ever! If anything I kept receiving ads about Verizon wanting me back as a client and all that. Now over two years after not dealing with Verizon, or having ever heard that I owed it money, comes this annoying, piddling threatening letter. The issue is not the money, I swear, I can very well just send a check and that's it. But I am very annoyed at such a huge corporation carrying on with these unsavory practices. Verizon has no respect for its customers. Why does it turn charges to a collection agency, two years after the fact without first notifying the customer. By the way, I noticed I am not the only individual who has written about similar incidents on this forum. Verizon: I would never do business with you, even if you were the last cellular phone providing company in the world!!