DTE Energy Detroit Edison, DTE, MichCon "FINAL BILL" is NOT final.. beware! Internet

On 7/2 I moved to a new address. I forgot to turn off electrical service at my previous address (my fault), however, when I left, I turned the master circuit breaker to the "off" position so that nothing could draw power. No one entered the home between 7/2 and 8/10 (date of shut-off)

On 8/10 I had my electrical service at my old address disconnect and a final bill mailed to my new address. About 8/15, I recieved a bill for the old address (at my new address) marked "FINAL BILL". I paid this bill in full on 8/17.

Today (9/16) I logged into my DTE online account to look at and pay the bill for my new address. I noticed ANOTHER charge on the old account (which was listed as "not in service" on the website), however I could not access a billing statement for the charge. I called in and spoke with customer service, who said that indeed the electrical was no longer in my name at the old address. When I asked about the additional charge, I was informed that it was the charge from the final date of last billing cycle (8/6) to the day electrical was shut off (8/10). I explained I had already recieved a bill marked "Final Bill" for that address and paid it in full. I was told that the bill was NOT the final bill (despite it being in BIG RED LETTERS) and I owed the additional amount (which was approximately 1/3 of what my usual bills were - in 4 days, with the power COMPLETELY turned off!).

To avoid a negative mark on my credit, I paid the additional amount today. Now I'm worried that there will be another fee next month, and the next month and so on.

If you can't trust that the bill marked "Final Bill" is really the Final Bill, what can you trust?

I've already submitted a complaint via the DTE survey, and have also filed a complaint via email. I'm seriously considering filing a complaint with the Better Business Burea of Michigan as well.

I'm not sure it is even legal (although, I cannot find a statute) for them to bill me again on the same account when they issue a "Final Bill" and it is paid in full. Is it?

(Any advice is greatly appreciated!)