Technical issue bad managed

I’m writing after countless hours being unable to navigate customer service. I got a new modem sent to me, which started causing my network to drop. I contacted customer service repeatedly, the AI would gaslight me that the network was fine, I connected with live agents many times, and they would also promise me either that they fixed the issue, or that there was no issue, or that the issue would not recur. Then they would disappear. I called, and the calls would also abruptly end. I went to the store and decided I had had enough and returned my equipment. As one would, I wanted to fully close the account and make sure I would be have a bill. They would not discuss with me as that is something I should discuss with billing department on the phone. So I call the phone, select billing, and it tells me I can’t access billing because my account is closed, and I should go online. I go online and the billing shows I have a balance and I should call customer service. This is a great way to lose my mind. I have already lose hundreds of dollars from missed meeting. I want to receive a refund for the 1.5 weeks I did not have reliable service, and a confirmation that my account is closed, no further balance is due.