It is in the TV. Talk to the TV and it'll battle you. It'll say "It looks like there's a Pokemon in the old TV! The Pokemon attacked! Rotom Noise" Or something like that. Bonus: Once you battle it, it'll be level 15 and in it's normal form. It'll know Electro Ball, and Hex, and a couple of others. Oh, I almost forgot! You can only come out at 4 PM - 8 PM.
So, here are the three possible reasons you didn't find Rotom
- It's not 4-8 PM.
- You didn't interact with the TV, and Rotom didn't appear because of that.
- You're game is hacked or messed up.