Verification by SMS is going to a number you no longer have
Switching phones doesn't always mean switching numbers. But when it does — a new carrier, a new country, a work line you no longer use — you're left with accounts pointed at a number that no longer exists for you.
In short: every account you set up with SMS verification or as a recovery phone saves that number on its own. Changing numbers doesn't update them all at once; you have to go account by account.
What happens
When you turned on two-step verification for an account, or set a recovery number, that number got saved there, independent of whichever one you use today. If you change numbers, every service keeps sending the code to the old one until you sign in and update it on that specific account. There's no single place that updates "all your recovery numbers" at once: not your carrier, not your phone, no provider has that complete list.
The problem shows up most when you actually need that second factor and the code doesn't arrive anywhere: the account asks to confirm by SMS, but the SMS goes to a number someone else may already have, or that simply doesn't exist anymore.
Why it happens
Because the phone number, as far as these accounts are concerned, is just another piece of data you gave at some point. The provider doesn't monitor whether you're still the owner of that number: it only knows that, when you set it up, it was yours. And it doesn't matter if that number ends up with someone else months later: many carriers recycle numbers that have been deactivated and assign them to a new customer, who would then start receiving your verification SMS without asking for it.
Who it hits hardest
People who switch carriers or countries and deactivate the old line without first checking which accounts use it. And people who used a number from a previous job, or a prepaid SIM that no longer exists, as the recovery phone for their email or their bank.
It also hits people who've had several numbers over the years (travel, carrier switches chasing a better rate, work lines that get shut down) and never do a general review: they find out, account by account and usually at the worst moment, which one ended up with which number.
What to check before you switch
- Are you about to lose access to your current number (deactivation, porting to a different owner, moving countries)?
- Do you know which important accounts (email, bank, social media, WhatsApp) have that number set for verification or recovery?
- Is any of those accounts also protected by an authenticator app or a security key, not just SMS?
- Have you checked the recovery number on your main email, the one that opens almost everything else?
If it already happened to you
If you no longer have the old number and an account asks for the SMS code to sign in, most services offer an alternative route once you explicitly say you can't receive that SMS: a recovery email, backup codes if you saved them, or a longer identity-verification process. There's no way to "impersonate" your old number: if anyone offers you a method to skip that verification, it's a scam.
Use the occasion to write down, account by account, what your current verification number is now. That way, next time you switch lines you'll know exactly what to check instead of discovering it by surprise.
Official sources: WhatsApp Help Center: two-step verification