Extreme buyers remorse.. and weird buying process

Hello yall, I usually dont make these types of posts since I stay in my lane in Lexus related posts but I couldn't help but to make a post here concerning one of my recent visits to a Verizon store.

To begin, I had bought a (very problematic) iPhone 16 pro max from a verified Verizon distributor (Brick and mortar store) In 2024 and that phone was nothing but issues, had a replacement, lags, internet cut out, froze, drops calls and messages, bad luck in general. So I decided to visit a Verizon store to just get rid of it, in hopes of downgrading back to an iPhone 15 Pro/Pro max which I had originally with no issues whatsoever. I go in, greeted, Explained my problem and that I want to downgrade back to a 15 Pro and then the Verizon representative does his stuff on the computer, tells me the Payoff price for my 16 pro max, the price difference of plans and phones (In this case a iPhone 17 pro) , and then all of a sudden he tells me that he "wasn't paying attention" and accidently signed something for me on the computer, and I was like whatever it might've been some random agreement or document, but he signed it himself (Scribble, not an actual signature) to have the iPhone 16 pro max to be paid off.

I then get hit with a 790$ something bill that I HAVE TO PAY OFF. He tried to call a couple of his managers to see what he can do, and they say that there's nothing he can do for me but I just have to eat the cost of the payoff and can't reverse it or it will absolutely destroy my credit score. I am forced to then do a cash advance on my credit card and take money out of my savings account and main banking to pay the bill. This leaves me in the bare and in a very bade situation where I am unable to make payments for my other unrelated bills, such as my Car Insurance that just was unable to go through so I can't even drive my car.

Fast forward to a couple of days later I have extreme buyers remorse and my Finances are in the dumps because of this one visit. Any advice on this or do I just have to eat the costs of his mistake and try to stay afloat? Thank you.

TLDR: 16 Pro max super problematic, I bring it into a verizon store to have it replaced by a 15 pro/pro max but I am forced to upgrade to the 17 pro but due to his mistake, and him signing the document that released the payment plan to me and I have to owe almost 800$ in a single visit that completely ate my finances and missed a couple of (rather important) bills. Walked out that day with a new iPhone 17 pro, 800$ down the gutter paying for a useless broken phone, and a hurt ego. Any advice would be helpful. Thank you.