The periphrasis dejar de has several uses in Spanish. The first use shows the end of an action or habit.
Dejé de fumar el año pasado.
I stopped smoking last year.
He dejado de asistir a clase por falta de tiempo.
I stopped going to class for lack of time / because I didn’t have the time.
It’s also used in the imperative form:
¡Niño, deja de jugar con esa pelota!
Boy, stop playing with that ball!
¡Por favor, deja de molestarme!
Please, stop bothering me!
When used in the negative form, it shows:
- A repeated habit
No he dejado de venir un solo día.
I haven’t stopped coming one day. (I came here every single day.)
No he dejado de practicar un día.
I haven’t stopped practicing one day. (I practiced every single day.)
- An ongoing action
No deja de repetir lo mismo.
He keeps repeating the same thing. (on, and on and on)
No deja de hablar de ella.
He keeps talking about her.
- As a piece of advice or reminder
No dejes de llamarme.
Make sure to call me. /Call me.
No dejes de estudiar español.
Don’t stop studying Spanish. / Keep studying Spanish.