You didn't do anything wrong.
But stories like this is why I ported my long-time cell phone number from my old carrier to Google Voice, THEN signed up with Straight Talk.
I researched the porting issue and it seems when American Movil is involved, it's just too risky.
I point my phone number to my Straight Talk phone and blithely ignore the phone number ST assigned me. If I lose my "Straight Talk" number, I don't care. It's not "my" number anyway.
No matter what carrier/MNVO I use, what phone I use, I will ALWAYS have my number. I just assign whatever device I want it to ring.
QUESTION: So, if you hear a Verizon message when your old number is called, Verizon doesn't somehow have control of your number?