According to one customer service supervisor, you have to pay the full month even if you cancelled your service the first day of the month.
Because I had to move to another state, I cancelled my FIOS internet service in the middle of the month. I had been using FIOS internet for 3+ years before the cancelation.
However, I already paid the one month in full, but I didn't get any refund back. I called the customer service to inquire the situation, and encountered supervisor (Michael). First, the customer service said my service ran for the full month. I clarified that I called verizon to cancel the service in the middle of the month, and I returned the modem on the same day.
Then, the supervisor (Michael) came in, and he told me I had to pay for the full month regardless. I responded that it is not fair because that means a customer had to pay a full month even if she/he cancels the service on the first day of the month for legitimate reasons. I also said I don't know how you guys run PR with this kind of policy. In short, he was very cold and inpatient, and I am not sure he was honest.
So I went ahead and researched the verizon contract, and I encountered a nice customer service person (Jacobiya). She was really helpful and willing to put herself in a customer's shoes. Anyhow, she filed a claim for me, and I will keep you all updated with the status.
Except Jacobiya, the whole customer service experience was terrible. I was treated with an unfair policy, and I wasted a lot of time. I don't know how this Michael guy was hired the first place, and how he was even promoted to be a supervisor. But, as I have seen before, strange things can happen in a big corporation.