You can't truly "permanently" block a number in a way that's irreversible, as blocking features are designed to be managed, but you can create a highly restrictive block by adding numbers to your phone's block list and enabling settings to block all unknown/private callers, essentially making it very difficult for them to reach you, even from new numbers by setting up stricter call blocking rules on your device.
Block a Number on a Cell Phone
Android: Open the phone app and tap the icon with three dots (⋮). Tap Call history and tap a number you want to block. Tap Block/report spam.
This Vertical Service Code, *82, enables calling line identification regardless of subscriber preference, dialed to unblock withheld numbers (private callers) in the U.S. on a per-call basis.
Block calls from specific people or numbers
Tap Contacts, tap a contact, then tap Block Contact.
Tap the three-dot menu icon, usually in the top-right corner, and select Settings. Tap Blocked numbers. Find the option for "Block unknown callers" or "Unknown" and toggle the switch to the right to enable it.
Dialing *77 on your phone activates Anonymous Call Rejection, blocking incoming calls from private or blocked numbers, making anonymous callers hear a message to hang up and try again. It's a landline/VoIP feature (like AT&T, CenturyLink) to stop spam/prank calls but can sometimes vary by carrier or state, potentially connecting to emergency services (like *87 to turn it off).
Block a number using Contacts
Here is the one big catch with blocking someone on iPhone: Technically, they can still send you a voicemail. Your phone will receive the voicemail, but you won't receive a notification about the message. Blocking someone on an iPhone still allows them to send you messages. You can read those messages if you'd like.
*74 | All Other Callers: Allow
All other calls (not otherwise specified in Call Handling settings) will be allowed.
The blocked contact won't know you've blocked them unless you tell them yourself, and the contact profile won't be deleted from your phone either.
Using an Android (Stock Android)
The classic option of dialing *67 before the number you're calling still works. This only blocks the call you're making at that moment, not any future calls. There are also a number of burner apps you can use to contact people without providing your actual number.
Blocking should, in most cases, prevent the perpetrator from sending your child more messages. Next, reporting the user brings it to the platform's attention, in hopes the perpetrator's account will be taken down or receive some sort of reprimand.
You're helping stop the scam for everyone. You have a few options to report suspected smishing: Forward the message to 7726 (SPAM). This works with most major U.S. carriers and helps them block scam numbers.
While it may seem contradictory, there have been instances where blocked numbers can still send text messages. These might not be specifically SMS messages. This situation typically occurs when a blocked contact uses a third-party messaging application that operates independently of the carrier's network.
Block Contacts in Settings in iOS 26
Tap Privacy & Security. Tap Blocked Contacts. Tap Add Blocked Contact, then enter the contact that you want to block. Tap Block Contact.
Block a number
Delete contacts
Open Contacts and tap the contact that you want to delete. Tap Edit. Scroll Down and tap Delete Contact then tap Delete Contact again to confirm.
Your blocked contacts will not know that you have blocked them.
For Android: Open the Phone app, go to Settings > Call forwarding, and enter an invalid number. For iPhone: Go to Settings > Phone > Call Forwarding, toggle it on, and enter an invalid number.