I also bought my phone from third party (Target) and got the same story you did about not qualifying for the port-in credit as a result. In making my purchase, I relied on the following thread (#842196) in this forum:
This question has been Answered.
theusualsuspect Nov 12, 2014 6:29 PM
Do you get the port in credit only if you buy online or in a Verizon Store? I found the devices I ordered 6 weeks ago locally at a 3rd party store, and wonder if I buy them at the 3rd party if I can still get the port in credit.
Correct Answer by Verizon Wireless Customer Support on Nov 12, 2014 7:53 PM
Great news! All port ins are eligible for this credit. It does take 2-3 billing cycles to get the credit, but going to a 3rd party vendor is OK!
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I will be following up with Verizon customer support now that I have located that post.