I am being double billed

I recently moved and had incredible headaches doing so. Your customer service, who I thought was helping me change my address, ended up adding a new address for my account so now I have two accounts and will be double billed. I did not intend for this. I simply needed to change my address and stop using the modem that had been provided by Xfinity, as my new apartment has their own. The customer service person told me I can hold on to my current hardware and use the apartment’s. However, setup did not work and the app does not let me use the apartment’s modem. This is way more difficult than it should be. I am willing to return the modems I have (I have two now, plus the one provided by the apartment, as during the last move there were other headaches that resulted in me being sent two modems), but I am paying $75 a month for service and I should not be getting double billed. I just want service at my new apartment and want to remove my previous one. Or, transfer service and undo the purchase your people just signed me up for in error.