upgrade digital adapter

I currently have a 2 year deal with a digital adapter at $7.99 and a dvr at $16.99.  I am trying to upgrade the digital adapter for an hd box without a dvr.  This should increase my bill $4.01.  Verizon wants to change my charge for my existing dvr from $16.99 to $12 and $12($24).  They say I am grandfathered in to the plan.  I am only looking to change the one piece of equipment not the other dvr or my current plan.  Is there any way I can just upgrade the one box without increasing the cost of my dvr.  This seems so simple but I cannot get any satisfaction.  It was ok for them to take away Cinemax from my plan when I was in contract saying it was no longer part of the plan.  Thank You.