Something similar just happened to me yesterday. My condo building has multiple providers: AT&T, Comcast, and Gigamonster. Apparently a Comcast technician "accidentally" disconnected my 1gbps Gigamonster service while setting up a new Comcast client in my floor's Telecom utility closet.
I've lived in highrise complexes for the past decade and have experienced this type of outage four times. The common denominator seems to be Comcast.