This is sounding like some primary school shit, no offense. I feel bad for this generation having to worry about cyber bullying.
I'll have to second Zangs here. Bullying people over shiny Pokémon is ridiculously childish.
My advice to you is: Treat this as the childishness it is. Make memes about it, then make memes
about the people bullying you about it.
I'll just say this though, based on the context you provided: You blocking them was not a nice move. Sent all kinds of wrong signals. If they considered it childish themselves, this can be like a drop of blood on the water for a shark. They might hammer on you just to see how more drastic you can get over a childish thing, and when you explode, claim YOU are the child for exploding over they'll claim to be just "silly jokes" after stalking you over and over.
This really is a case I would argue it's best to either ignore, or join on the silliness. The very nature of the situation can be misconstrued as "just this retard losing his mind over pokémon grow the fuck up" when it really is a case of people using something silly to really torment someone else.
About your youtube channel: If you're afraid of this costing you your channel, meme the Shiny Meowth before anyone else does. Make it into your joke before anyone tries to take it away from you.