Difficulty setting up Xfinity internet using a former DirecTV cable

I recently moved into a new condo and have been trying to setup my home internet. The unit is wired with 75 ohm RG6 coaxial cables, with one leading from my unit (on the third floor) to the basement of the building, where it connects to another coaxial cable coming from the Comcast box in the alley. The cable connecting to the Comcast box used to connect to a DirecTV satellite dish on the roof of the building. When the first Xfinity tech came out to setup my service, he cut this cable, crimped a new connector onto the cut end, and connected it to the Comcast box. When I try to connect my modem, a downstream connection is established almost immediately, but an upstream connection can never be established.

Two Xfinity techs have come out so far, and neither were able to resolve this issue. The second tech that came tested the connecting wire with a multimeter, and the wire is live (though I've since read that multimeters are not great for detecting damage to coaxial cables). Both techs confirmed that the coaxial cable coming from the Comcast box has a solid signal. 

The cable seems to run in a conduit from the basement to the upper floors, but I do not know where the conduit terminates. I've tried pulling gently on the connecting wire at both ends, and it does not budge, so it is likely stapled or caught on something inside the wall. I've asked the HOA for a wiring schematic for the building, and they've been entirely unhelpful. I spoke with the previous owner, and strangely, she said that her DirecTV service was working fine before she moved out, and that service was using all the same cables. Both techs also replaced the connectors at both ends of the connecting cable.

Is there something I'm missing here? Is the only solution to route a new cable directly into my unit from an exterior wall?