Sprint PCS Unlimited Data Plans...

In October 2011 I paid a visit to Digital Highway, my Local Authorized Sprint Dealer, with an issue. I needed a solution for providing internet to my home network. The cellular plan I have, Family Share Everything 1500, provides for unlimited internet via a hotspot I have had active on my phone for a year or so, with the ability to connect up to 8 devices. My Local Authorized Sprint Dealer took a look at my situation and provided me with the following resolution...
Add a 5th line to my current plan, use that 5th. phone as my personal cell, and use the phone that has the active hotspot as my internet. After weighing the few options I had, I decided I would follow the advice of my Local Authorized Sprint Dealer, and do what they advised me to do. So I added a 5th line and spent approximately $500.00 to add and activate my new phone. In a letter from Sprint, dated Dec 30, 2011, Sprint informs me that I use too much of my "Truly Unlimited" internet and as of Jan 31, 2012, 4 months into the solution from my Local Authorized Sprint Dealer, they will be changing my contract and place a 5GB per month limit on my "Truly Unlimited" contract and charge me any overages. I called Sprint to get clarification on what "Truly Unlimited" meant to them and how they justify breaking the original contract and limiting my internet with the lowest plan they offer and no compensation for taking what I have been paying for, "Truly Unlimited" and forcing the smallest data package they offer on me, with threats of a bill for $2000.00 for the OVERAGES that have already occurred. How you acquire overages, of any amount, on an unlimited plan, is beyond me.
So I am left to decide how to move forward, take the fact that I was either misled and/or lied to by my Local AUTHORIZED Sprint dealer and Sprint PCS feels they can just change contracts to suit them whenever they feel the need. Not to mention the $500.00 out of pocket to add another line and another 2 year contract, plus an additional $75.00 per month that my now unneeded phone line cost. Apparently a 20+ year relationship with Nextel and Sprint and paying them $300 - $400 per month for what they are contracted to do, means very little to Sprint PCS.