Reliant Energy-Houston Guestimated Billing???? Houston, Texas

I paid my utility bill in full and had a $0 balance as of 2/15/10.  I received a bill in early March 2010 for $4 and some change.  I was worried this was a mistake so I asked Reliant Energy to send a technician out to check our utility box.  I then received a bill indicating a current due of $787.38!!! When I called Reliant Energy to ask about this bill, the representative advised me that a Centerpoint technician changed my utility box on "what she believes" was March 4th and "discovered" that my utility box had been breaking for some time-???  We had been receiving regular bills and nothing had been wrong- we were paying averages of $250-$350 month without fail...... According to this representative, the technician "discovered" that the utility box had started to malfunction sometime in November 2009 to the best of his "knowledge".  So, Reliant Energy decided to look back at our usage from the previous November 2008-February 2009 to determine what we ACTUALLY could have been using for the months November 2009-February 2010.?????..... and they invoiced us for the difference of what we had already paid..(Remember I had already paid this account to ZERO BALANCE as of 2/15/10. ) So here I am stuck with this outrageous guestimated bill??? To make things worse, this ever so kind representative advised me that the Centerpoint technician said there was tampering with the box so now our account was NOT eligible for a deferred billing offer???? WHAT????  Noone has tampered with that box!!!!!  However, I sure do feel strongly that someone has tampered with my account and my money!!!  This ever so kind "customer care" representative also advised me that if I did not pay the amount in full we would receive a disconnect notice and charged a disconnect fee--gee thanks----