It's, alas, difficult to solve something against the victim will.
I'm sure that in all countries you can easily find cops with such stories.
"I can't leave him, he would find me and kill me this time", "what would my family think", "the children, you thought about our children ? They need a father", "it's not with my poor salary that I would be able to raise the kids", "divorce is against my religion", and so on.
Of course, most of the time you can find rational arguments to counter the reason gave to not leave him. But it's not a rational situation.
It's a relationship that started with love, and the victim is generally still blinded by what rest of this love she had for him. The reason they give to explain that they stay are generally her way to not face the fact that they've been abused (not physically) and fell in love for someone who never deserved it. And when they face that fact, they usually do it, at first, the wrong way, believing that they were stupid and that all this is their fault ; what isn't at all the case.
And, as I said, for some it's a pure question of money. What is better ? Living with someone who, too often, is violent with you, or living on the streets surrounded by strangers that you imagine ready to violently rape you anytime they want ? When there's kids it's worse, because as a mother you want the best possible education for them, something they can have thanks to their father job, and would not have even if their mother had the chance to found a second job.
So, yeah, staying with your abuser, while taking some precaution like a hidden phone, is, alas, not something exceptional...