How long ago was the initial mistake? If it were more than 30 days ago, you might be stuck, because you will have to prove it was a mistake on Verizon's part? People actually upgrade using the cross upgrade thing, so it would have to be proof. If it were long ago it is likely nothing you can do. Because when you noticed the mix up you let it go instead of having it corrected.
If it was recent I would call customer service and escalate until the problem is fixed. At any rate I would call customer service explain this issue and escalate as high as you can especially if it is not your fault.