Blame Cogent, not Sprint
https://www.sprint.net/cogent.php
Based on Cogent’s history of fucking up a peering session, routing any traffic destined for their former peer into a black hole, then crying and screaming about it, I tend to believe Sprint’s version of events. In this case, it seems Cogent was refusing to pay their bills because they didn’t qualify for settlement free peering. If you or I didn’t pay our bills, we’d get turned off a hell of a lot faster than Cogent was.