Internet resets every 2 minutes!!!

For 3 days now my internet has been stuck in almost a loop. Disconnect...reset...disconnect...reset..etc...my router/modem shuts off completely and reboots. We have spent close to 20 hours on the phone with at least 10 reps. All telling us different stories. Some refusing to escalate our issue because they all had the same training and there are no tech specialists or experts...of course supervisors are always busy on the other phone so they don’t want you to talk to them. I question if it really is a supervisor. All want to go through the same troubleshooting with us. Nothing fixes it. We though it was the router so we went out and bought a new expensive router/modem thinking we would fix the issue. Immediately, the problem continued. Comcast seems to have no idea what is going on. Customer service just reads scripts and sends a signal. One told us we had some error code. Then the next one said there are no such thing as error codes!!! That was the same one who said there are no such things as tech support specialists or experts!! They refused to send a tech out. Reading the forums, it sounds like I am not the only one with this problem and doesn’t sound promising that there is a fix. Anyone out there have this problem and actually had it fixed???