I assume you are doing this from the Verizon page as I did, and had the same issue yesterday. What I figured out was: once I opened the link to acc. pack it was priced at 19.97, however I clicked on the details tab (or more info? whatever it was named) to read about what all came with it and then I added it to cart from there and the price went to 49.97.... I then backed out all the way back to the original tab where the price was advertised at 19.97 and added it to my cart from there and the price was 19.97 then. I removed the $50 from my cart and proceeded to checkout. Give this a try and hopefully it will work for you.
Nearly bought one today but can;t get the $50 (used to be $100!) off until July. So I'll wait.
If you started your NE2 plan before they dropped it to $50 then you're grandfathered in. I had to talk to a supervisor, it's actually your original contract they need to honor than being grandfathered.