convert 3g to 4g mifi without losing unlimited Verizon data?

I have never had trouble, with a corporate Verizon store, or with customer service
Added value retailers are a different league
I bought my last new phone Samsung Nexus, out right, so I could keep my unlimited data plan.

You buy the new device ..Then you have it activated on your current plan
You do Not do an upgrade, you do Not buy at a discounted price, you do not even have to sign Any contract papers