It would really help to know why, exactly and in detail, you believe that your modem-router is compromised.
I'll be honest and say I'm not completely sure but I can say that the behavior with my connection does not seem normal.
I have no experience with this so I cant be sure. My routers admin account password keeps getting changed or I just keep ending up unable to log in. It keeps happening even if I reset from the reset button from the router (The little small one that is suppose to reset all configurations). There is also a remote management tab in it which when I disable all remote management rules (All of them seem to be fine until I disable remote management via DNS) my network goes offline and I have no internet. I had believed that maybe this was some sort of backdoor my ISP had set, but they said I should be able to turn it off. I see a lot of intrusion alerts and DOS alerts but I figured maybe that is normal as its being caught and rejected, but the fact that a few weeks back my laptop was remotely controlled, also a day before it was remotely controlled I had kept an eye on wireshark and saw that whenever I had opened Firefox no matter what website I visit, there would always be a connection trying to connect to my router. I'm a novice with using wireshark so I cant analyze everything but that I could tell that it was trying to log in as it was pointing to my routers local ip, and viewing the data it was trying to access it. It was constantly trying to access it as long as firefox was open. I can send you a PM of the printscreen I took that time.
As to why this is happening?
I do not know, I'm a young adult that has barely any money to survive yet it feels there is some stalker or hater that is out there trying to ruin my life. Maybe I'm just getting paranoid out of the fact that my laptop had been remotely controlled and what I saw in wireshark.
If you know any signs of being compromised I would be grateful to know so I can keep an eye out for these signs.