In this case, the pin you are routing to is internal to the pad macro. It looks like this pin is surrounded by blockages.
Again, turn on "Instance Pin" and "Cell blockages" and start turning on/off each metal layer to get a pickture of what the routing/blockages look like inside the macro.
Just a thought .... You said this is an IO pad cell. What pin is this? Where is the other end connected to? It looks like its name is "pad" which makes me think this is the pad pin that gets connected to the outside of the chip. If so, there shouldn't be any routing on this. Check your verilog to see if this gets connected internally, or if this gets connected to your top level port list.