"Stop using the internet!"
Translation:Berhenti menggunakan internet!
That would have a different meaning. Using /hentikan/ would be including the causative/benefactive suffix /-kan/ on the end of the root, so it would sound as though you were telling the hearer to cause someone or something else to stop using the internet. If it's the hearer who is using the internet (whom you would want to stop by saying this), then, no, you wouldn't use /-kan/.
However, you might using /hentilah/ instead for the purpose of more strongly emphasizing the verb as a command.