Yea but if you change your MAC address to an unregistered one (what happened when you connected a new modem) you won't get internet and if you change it to a du

Yea but if you change your MAC address to an unregistered one (what happened when you connected a new modem) you won't get internet and if you change it to a duplicate one your account will be suspended (unless you're doing a swap like in your case). You can't have 2 modems using the same MAC simultaneously.