When someone first changed the MAC from the original, it should've made a backup. I've never had it restore those certs automatically, but you can go and restore them manually from one of the other tabs. You're looking for a file called CM00xxxxxxxxxx.tar, you should be able to manually restore certs from that, and the xx's should be the matching MAC. Obviously, change your MAC to match it.
Having matching certs and MAC, you should sync again, and be in TWC's registration mode, where all traffic is redirected to a signup page. The obvious work-around for this still works, and since you can force configs still in some TWC areas, you may not even be stuck at the sub-1mbit speed.
And that is probably far more help than I should give to someone who registered this month, but hey, trying to stop lurking so much...
Having matching certs and MAC, you should sync again, and be in TWC's registration mode, where all traffic is redirected to a signup page. The obvious work-around for this still works, and since you can force configs still in some TWC areas, you may not even be stuck at the sub-1mbit speed.
And that is probably far more help than I should give to someone who registered this month, but hey, trying to stop lurking so much...