No you were not at all wrong, penning a letter and hoping to get some answers to the sense of loss you experienced throughout your life.
It's a bit, 'the least he could do'
Unfortunately step families can be horrible and I personally think this woman needs a good reprimand, are you going to listen to her, who the hell is she to forbid correspondance, I woudn't dare get involved with a father/daughter relationship no matter the estrangement.
She could be protecting her financial interests and keeping you at arms length from ever reconnecting, I've seen this happen.
I'm sorry you experienced such twattish behaviour, none of this is your fault.
Sounds like the people in his second life suited him, nasty people.
Maybe write a letter to her, and tell her your views on her and her letter writing, sitting on her high horse, she's a joke, trying to protect him. You have every right to correspond with your father, I honestly believe society needs to change it's views on protecting these men.
Accountability affects everybody in all ways in life why should feclkess dads be any different, let them know before they pass on.