I moved out of my apartment in Dec of 2016, and ca...

I moved out of my apartment in Dec of 2016, and called to have the electricity switched back to the landlord. I was told by national grid that the landlord had to call to switch the apartment to their name, not me. I contact the landlord and they tell me that they have taken care of it.
Fast forward to April 2018, my husband and I are moving into a new place, I call National Grid to switch the electricity there to my name. I am told by the customer service rep that they can t because the apartment from 2016 is still in my name and has been all this time (mind you I never received any notice, phone calls, nothing regarding late bills in the last year and a half that I was no longer living there). I call the old landlord and come to find out, the new tenant was just throwing the bills out that kept coming in my name, and never paid any of the electricity that they were using.
At this point I fill out a dispute with national grid, to provide proof that I did not live at that address during the time in question, and to provide proof that I requested an end in service at that address. I provided notarized statements from where I actually lived, bank account information with my actual address, among other things and even provided a notarized statement from the landlord at the address in question stating that THEY are responsible for the bill, not me.
Today I received a letter from national grid, stating that my dispute is being rejected and that I am still responsible for the full amount (over $1000 dollars). I am astounded by the lack of accountability and responsibility this company shows. I imagine they only treat their customers this way because we have no other option for service in this area. So much for Thank you for calling National Grid, here with you, here for you. That couldn t be further from the truth.