Seneca,
I’m wondering if there’s a nuance that I’ve missed before now, between Fortune and Fate. This polemic against Fortune seems as suited to a Cynic discourse against Fate. I suppose the snide among us might say, “There is a difference, you can tell, you know, because of the spelling.”
“[G]ird yourself about with philosophy, an impregnable wall. Though it be assaulted by many engines, Fortune can find no passage into it.”
We have the (later dubbed) amor fati component of the Stoic worldview, and if Fortune and Fate are used interchangeably, this kind of charge seems to be a contradiction.
Instead, if we look at it as Fortune being the fickle nature of externals in relation to ourselves, and Fate being the divine order, that apparent contradiction vanishes.
“The soul stands on unassailable ground, if it has abandoned external things; it is independent in its own fortress; and every weapon that is hurled falls short of the mark.”
This seems to be the case, then. The Stoic instructed by you, Seneca, accepts whatever Fate brings, and attempts to set aside the things on which fickle Fortune preys.
Fate versus Fortune will be interested fodder for the day.
Farewell.
Mountain Stoic 
There is no Amor Fati in Stoicism. Fate is an indifferent and the prime example of things we have no control over.
The phrase is not Stoic, that much is true. But I think you’re mistaken.
“They too [Zeno and Chrysippus] affirmed that everything is fated, with the following model: When a dog is tied to a cart, if it wants to follow it is pulled and follows, making its spontaneous act coincide with necessity, but if it does not want to follow it will be compelled in any case. So it is with men too: even if they do not want to, they will be compelled in any case to follow what is destined.”
– Long and Sedley 62a
They wise person then chooses that which is necessary. That often gets parsed as a love of Fate.