Anyone else not getting Internet after an upgrade

I'm curious if anyone else has been booted off their network as a result of an upgrade. We upgraded our modem last Saturday and have not been able to get online since, after daily calls to Xfinity and four technician house visits. I've heard that we should not have upgraded becuase our old modem was already in the network. Because more and more people started working from home, the network reached capacitiy. Even though it was at capacity, my old modem was hooked into the network, so it was fine. However, when taking the old modem offline, getting a new modem, and trying to get it online, I have been told that it can't get online becuase it's new and the network is at capacity. I really wish the person I spoke with on Saturday told me this. Does this sound about right?