One of the ways to kill a process on a port is to use the python library: freeport (https://pypi.python.org/pypi/freeport/0.1.9) . Once installed, simply:
# install freeport
pip install freeport
# Once freeport is installed, use it as follows
$ freeport 3000
Port 3000 is free. Process 16130 killed successfully