Sounds like you should have just went through that last month of service rather than cancel it. Would've been cheaper. If your contract term results from your purchase of a smartphone, your early termination fee will be $350 minus $10 for each full month of your contract term that you complete.
Companies with large accounts like when I was in charge of cell phone services for the state have an Account Representative in fact I had two of them. If you speak to them and request to have it overridden I am sure for the loss of 100 corporate phones and devices that is enough money loss to get their attention and no early termination fee.
Call the account executive and inquire.
Hi, BC__NYC, it doesn't make sense that you would be charged an early termination fee if you are, indeed, canceling your contract during the final month of the agreement (i.e., before the last day of the month). Did you read the FAQs on early termination fees. They make clear that if you cancel your contract, the cancellation will not take effect until the end of the month--and you are responsible for the full month's charges. You may want to see if your state's Attorney General's Office or consumer protection office may provide an avenue for you to dispute the charge.