CRJ-700 Captain reported that the Flight Attendants were having difficulty closing the main cabin door. After contacting Maintenance Control; Contract Maintenance Technicians discovered the ice breaker cable detached and broken.

Narrative

Aircraft X departing ZZZ to ZZZ1. We finished boarding and I heard the Flight Attendants struggling to get the Main Cabin Door closed. After multiple tries; I left the flight deck to see what was going on and try it myself. Multiple more attempts; we could not get the door to close and I contacted Maintenance to write it up. They instructed me that this was a recurring issue with this aircraft. After writing it up; Contract Maintenance arrived at the aircraft and started troubleshooting the issue. They were able to get it closed and latched; but I mentioned that the FAs (Flight Attendants) should be able to close it. The Contract Maintenance was in touch with Maintenance Control and was told that it was likely due to uneven ramp surface and that if it closed; they would ops test it good. We moved the aircraft back a little bit and still encountered the same issue. Contract Maintenance realized that there was something wrong with the handle or door as well and the Flight Attendants were still not comfortable with it. They insisted something was still wrong. I told Contract Maintenance that I was not okay with an ops test good because it was an emergency exit door and was not working properly; whether it closed or not. After urging them to further troubleshoot it; Maintenance Control instructed them to remove a panel and check a cable. They inspected it and found that the Ice Breaker Cable was snapped. They explained that this cable was to assist the external handle open in the event that it iced over during flight. Without this cable; it could possibly not open during an emergency and no one would know about it. This aircraft flew multiple times after being written up multiple times and being ops tested good previous times. Fortunately; we urged them to dig into it further and corrected a huge safety issue.We should not be so quick to perform ops [checks] and mark them successful without troubleshooting further. Maintenance Control complacency on understanding this is an emergency exit and should be thoroughly troubleshooted. They assumed incorrectly and could have resulted in life threatening consequences in the event of an emergency.