I cant't activate my Iphone 7

Before, my phone has no cellular service and it requires me to download and install newest OS. After i downloaded the OS, it doesn't allow me to install. I got so ******, so I click restore factory settings because I thought that would help. But things get worst after, I can't activate my phone. Tried to connect to pc and Itunes to update and restore software. But ended with the prompt " The Iphone could not activated because the activation confirmation could not be obtained from the device. Disconnect your Iphone and make sure the SIM card is inserted correctly."

I am very frustrated right now. Wasn't able to use my phone since August 2020.

Please help me on what to do. Thanks