Duke Power of Charlotte NC SHADY BUSINESS ETHICS, Internet

To Whom It May Concern:
 
In May of 2008, I contacted Duke Power's Customer Service to inform them that I would be leaving at the end of May, and to arrange for the forwarding of my Security Deposit of $150.00, and the final bill. 

At this time, I had a current balance of approximately, $41.00 which after paying left me with a 0.00 balance.  About one week after placing this phone call to Duke Power, I received in the mail a letter, basically stating:  "That I would not be receiving my Security Deposit, because of some "supposed" malfunction of the meter. 

To add insult to injury, they topped the letter off, by stating that I "owed" them $500.00, and that they had "approximated" what I owed to them from other residents "usages". 

I was highly upset by this since as I stated above, I had a zero balance with Duke Power, I am permanently disabled and receiving SSD, a single mother, and on a fixed income! At any rate I moved out of State, for over 1 year. 
 
Due to circumstances beyond my control, I was forced to return to Charlotte to live.  On Thursday, November 5, 2009 after having lived in the State of Maryland for over a year, I contacted Duke Power once again, to discuss the Security Deposit issue. 

I spoke to a woman by the name of Maritza (spelling) who essentially repeated what was told to me the previous year.  She then went on to "explain" the bill to me, and stated that my July 2008 bill was $85.00, that my meter was "replaced" on 5/12/08, and that my bill for May was approximately $41.00.  And that I should have taken "note" that my bill was too low. 

That was shocking to me to say the least...as I'd been out of that unit since the last day of May 2008, just as I'd stated to them the previous year!  The family that moved in behind my 2 person family, was comprised of 4 people, and in one of the hottest months had a bill of $85.00!! 

This also was interesting...since she claimed that Duke Power had "approximated" my bill, leaving me with a whopping $500.00 bill, and preventing me from getting my $150.00 Security Deposit!  This too was interesting to me, because the family of 4 had a bill of $85.00 and my family of 2 had a bill for approximately half of that!  Yet I should have been suspicious of this bill...per Maritza!! 
 
I'd like to know...what Duke Power is going to do to resolve this obvious error on their part, and to protect me...the consumer??