Switched to shared plan-bill on old account sent to collection agency without notice!

Question

On 9/16/12, my husband and I visited a Verizon store to upgrade our phones and enroll in a 2-year renewal contract, as we have done for years.  While speaking with an in-store representative, we were encouraged to combine our plans into a family shared plan. We took the necessary steps to do this and my husband moved his account to combine with mine.  From this point onward, we paid one bill together. We assumed my husband’s account was correctly closed and never heard anything else about it from Verizon.   We were therefore unpleasantly surprised to receive a letter from a collection company demanding that he pay a $135.63 charge from his old account that we previously knew nothing about.
I have been a loyal customer since 2003 and have never missed or even been late on a payment throughout this time.  To find out that there is a delinquent account sent to a collection agency which will affect my family’s credit is very disconcerting.  Further, to read stories from former Verizon customers saying that they too had received letters from collection agencies regarding unpaid bills that Verizon never alerted them about leaves me wondering whether the procedures for closing an account are being properly conducted.   In our case, the situation is even more frustrating since we are not former customers that Verizon had trouble contacting regarding outstanding charges.  We are current customers who would have been happy to make a payment had we been aware of it in writing.  A simple search would have shown that my husband’s phone number is still valid and is now part of my account in our shared plan.  We would have expected to have either received a bill addressed to him regarding a final bill that was owed on his old account (he used auto-pay while that account was active) or to have had the final charge moved to my current account, since I am now the primary account holder with both of our phone numbers under one plan.  It would seem surprising to send a bill to a collection agency when dealing with someone who is a current customer.
There is no issue with making a payment directly to Verizon as long as our credit is not affected.  We have written a letter to Verizon but have not received any response from them in a month and a half. Has anyone else successfully dealt with a similar issue?
Thank you.

Answer 1

He didn't receive a hard copy because he had paperless billing set up (as well as auto pay).  We checked his email for any billing statements sent and there were none after the account was closed.  As SydneyK mentioned, since he only had paperless billing, after the account was closed there was no way to access it online and see that there was an outstanding balance.  In fact, the Verizon representative stated that his account would be "moved over" to mine, which to me implied that everything, including a balance, would be "moved" to the shared plan. We finally figured out what the outstanding balance was for - for the new phone he upgraded to when we went to the store to upgrade our phones and switch to the family plan.  They had charged his account for the phone, rather than my account/the shared account. Ugh.