Prefix Not Working

I had this working before, but suddenly it isn’t working, i might have made some changes to the code I’m not sure.

client.on(‘message’, message => {
let args = message.content.substring(prefix.length).split(" ");

switch (args[0]) {

case "ping":
        client.commands.get('ping').execute(message, args)


case "help":
    client.commands.get('help').execute(message, args)

Show us the code where prefix is defined. Also state how it’s “not working”.