First of all, I am sure you will definitely get 1 million likes. There are several people who dislike Verizon, but even with 1 million likes, that still means less than 1% of their customer base. And I am sure several of those likes will be from "former" customers like yourself which would mean an even smaller percentage.
Maybe it happened different than you described, but the way you explained your story you did not ask for the policy on cancellation of service. You asked "I told her that I’d have the T-Mobile phones on Friday (July 12th) and I'd be porting over the lines then so I'd only owe $75.00 and a "few days of service, right"?" In this explanation, you are not asking about the policy. The statement is correct, problem with your question is you did not ask if Verizon bills for "partial months". Unless there is something you are leaving out, you also DID NOT ask for the policy on service cancellation. Yes, you would be paying for a "few days of service" but the smallest increment when you cancel service is to the end of your billing cycle. The ONLY time you ever receive a bill for a partial month is when you begin service with Verizon. NEVER when you are a current customer.
You said you talked "at great length" about how services are paid including I assume paying a month in advance for service which is how Verizon has done business for as long as I can remember. You also say your bill closes on the 7th of the month. Well that means Verizon would have "billed a month in advance" for your service on July 8th. Now you may have said you were porting on July 12, but Verizon does not have a crystal ball and not all customers follow thru with their plans. When you request a port from another provider, Verizon does not cancel your service UNTIL the port takes place. They do not cancel your service and then trust the port will proceed on the specified date. Since Verizon would have billed you for a "month in advance" on July 8, did you also ask if you would get a refund of a portion of your bill? You don't say you asked that question, but you may have done so. I assume you didn't, otherwise you would have pointed that out I suppose.
It is doubtful you will get any pro-rated credit on the remainder of the billing period, but good luck anyway.
I am in no way trying to be pro-Verizon here as I have been labeled more times than I can count. Just trying to point out Verizon's policies are easy to find in the contract. Also anyone on these forums would have been able to give you the correct information.
I am aware there are several people who claim to have been lied to by CS reps. Whether it is a lie or simply a misunderstanding, I don't know as it has NEVER happened to me in the many times I have interacted with CS. Of course, I try to research the question prior to asking CS if they give an answer which contradicts the contract or a "partial" answer which sounds like what you may have gotten when they confirmed you would be paying for a "few days of service, right". Technically, that statement is correct, but what they failed to explain to you was that you would have already been billed for a full month and would not get a refund. Technically when you spoke "at great length", this was explained to you, at least as you have mentioned in your story. As this part of the question may have been several minutes from your question about pro-rating, you may have thought it didn't apply. Quite possibly a simple misunderstanding, I have no way of knowing. Partial answers when you fail to ask the correct questions sometimes sound like lies.
Finally, good luck with your new provider if you choose to stay with them.