If neither of these router models work on this cable ISP system, could be a incompatibility with them or something on the ISP side has changed.
Can try setting the WAN port speed to either 10 or 100 or 1000Mb and see, test each one out.
If you have a friend or family member who has internet, take these routers to there place and test them out. If they work there, then the issue is with the ISP possibly.