$100 extra charge

Hello, I was wanting to reach out in regards to the $100 charge on my account for the tech visit. I was sent an replacement modem that was upgraded. I was able to activated it and it ran fine for an few hours until it went down. After working with support, they sent an tech out who mention that the XB7 modem had an history of issues and replaced the modem and got me back online. I was questioning the $100 as I was told in chat by Xfinity that I would not be charge if this was an Xfinity issue,