Dropped internet connections

Since Xfinity sent me their "new and improved" modem, I keep losing internet connection. I get the pop-up asking for my PW; I enter it and a moment later I get the same pop-up. When I've had a connection, I've contacted Comcast and have received no help whatsoever. I've been waiting for a call-back for three days now and have heard nothing. I demanded my old modem back -- never trouble with that -- or a new modem, along with reimbursement for all the time lost and trouble I've been through. No response. In addition, my landline phone began ringing once and then, nothing. I learned that callers were receiving two different types of message: one that stated the "system is not available" ; the other directed callers to a phone number that is not mine. I contacted Xfinity; stayed with them for close to an hour without results. "I'll have a tech call you." That was three days ago. WORST COMPANY I HAVE EVER HAD TO DEAL WITH.