Are you talking about the feed line to the control valves for the ref, or the lines from the valve(s) to the dispenser/ice maker? If it is the feed line, there could be a shut-off valve in the line, probably under the sink where it feed from. If it is actually plugged and you can get to the other end of it, try running a small wire through it, like MIG welding wire, to unplug it.
Good luck.
Wildmanbaker