The completed sentence will be:
En la casa de su amigo
TOMÁS:—¿Vamos a ver el programa musical en el canal 7? ALEJANDRO:—¡Qué pena! Ellos acaban de cancelar el programa para esta noche.
In the given context, "acabar de" is used to express that an action has just been completed or happened very recently. In this case, Alejandro is conveying that the television channel has just canceled the musical program for the night.
So, when Alejando says, "Ellos acaban de cancelar el programa para esta noche," it translates to "They have just canceled the program for tonight." The phrase "acaban de" emphasizes the immediacy or recent occurrence of the action, indicating that the decision to cancel the program was made very recently.