I think one of the problems is that I don't know what you see on Cloud MQTT. I use mosquito, and if I publish to "/MCThings/test" I see that in my subscriptions.
One thing that is a bit of a challenge is that you can only publish ListOfByte objects, but the examples should all work.
You have to do the following:
Dim payload As ListOfByte = New ListOfByte
payload.Add("test")
Lplan.Pubish("MyTopic", payload)
Then look for "MyTopic", I publish once per 10 seconds minimum, don't do less (say 1 second) as it doesn't work. You can't hit the gateway with lots of publishing one after the other. Eventually the module just stops publishing.
Ignore the mcThings/XXX stuff, that's just beacons from the modules showing they are alive (you can put data in the beacon, but walk before you run!).
Hope this helps.