Children call my daughter, laugh at her and hang up?

My daughter's friends—two siblings, ages 12 and 10—have moved, and my daughter gave them a final gift: a sweet photo album as a keepsake.

Ever since they moved—I don't know why, of course, you can't force it—the sisters haven't contacted my daughter since, even though they've known each other for ten years.

As I said, okay, I completely understand. You can't force someone, but now they're calling my daughter and making fun of her because they know full well that my daughter calls them all the time. Does that also make you feel appreciated?

I told my daughter, "Okay, for whatever reason, if they don't answer your calls, don't call or answer anymore." In the last two or three times, they've called, laughed at my child, made a fool of themselves, and hung up. This has happened three times now. My daughter is hurt, and I raise my children so that they don't hurt anyone. Should I tell their mother? I think that's bullying.