I'm not really all that sure it's useful what you are doing. You only check on join, and you tell them exactly why they got banned. The only thing they have to do is leave that other channel after 5 minutes, join yours, and then join the blacklisted channel again. If you don't want ppl inside your channel that frequent another, just banning them without too much info is better (like not saying for how long and what particular channel).
However, if it is just to try and keep out bots you know are in a particular channel, and that don't understand kick messages, then I shut up
Which I'm sure this is actually for, so maybe this post is what was useless
