Why did Verizon give me a credit on the shortfall charge?

[Webfeet]

This is strange.  I had Verizon local landline service and a separate long distance service with AT&T.  Yes it is strange I had the two services but it wasn't my doing, it was the result of years of corporate mergers, acquisitions and splits.  I decided to simplify by dropping the AT&T long distance and add long distance service (5 cent plan) to my Verizon account.  I now have the crazy shortfall charge being added to my bill which is anger inducing.  What is strange is that Verizon seems to have given me a one-time $66 credit on the shortfall charge which only appeared on my previous bill.  Why did Verizon give me this money and then continue to bill me the shortfall charge?