I'll assume you're at least using a Samsung phone since you're here on this forum, but the below suggestion applies to all models.
Go to the phone app (that green icon you open to dial numbers for calls) tap the three vertical dots on the upper right hand corner on the screen and then click on settings. Scroll down to "Supplementary Services" and click on "show your caller ID" and then click on "Never". When this is selected, whenever you call a number it will show up on their end as " private number" and they can't dial or call back because there won't be any number there to dial.
