打错了。

Use it the moment you realize the person on the line is looking for a 'Mr. Wang' you have never heard of. You can say it alone or add a polite 'sorry' before it. For example, 不好意思，你打错了. It is short, so you do not need a long explanation. Just say the phrase and wait for them to apologize. It works for both voice calls and text messages.

Use it when a stranger calls your mobile at 3 AM. Use it when a delivery driver calls the wrong customer. It is perfect for those awkward seconds when you both realize there is a mistake. In a professional setting, it keeps things brief so you can get back to work. If you are texting, it is a quick way to stop a thread of accidental messages.

Do not use this if someone makes a mistake in a conversation. If they say 2+2=5, do not say 打错了. That would sound very confusing! This phrase is strictly for telecommunications. Also, do not use it if you recognize the caller but they just have the wrong information. In that case, you would correct the facts, not the phone number itself.

In the old days, people actually 'hit' buttons or turned dials on phones. That is why we use 打. Chinese culture values efficiency in these small interactions. You do not need a five-minute apology for a wrong number. A quick 打错了 is considered helpful, not rude. It saves everyone's time and battery life. Interestingly, 'wrong number' scams are common now, so saying this firmly helps end those calls quickly.

If you want to be extra polite, add 您 (the formal 'you'). You can say 您打错了. If you are the one who made the mistake, you say 我打错了 (I dialed wrong). If you want to ask if you have the right number, you might say 是不是打错了? (Did I dial wrong?). It is a very flexible little phrase for any phone-related confusion.