If you can move it a foot there is hope. My guess is that the original installer taped the two wires together. This should never be done when pulling wire in a conduit because they can bunch up if one wire is longer in the pipe. Try pulling each of the old wires separately until all slack is removed, then pull both together. Wire lube (Home Depot) is helpful but it may not reach your tight point at first. You could blow, squirt or vacuum the wire lube into the pipe. Be very careful not to break the old wires by tugging too hard. As stated above it is best to pull in a string first, then the new wires.