1. Wrong number: Maybe you touched the phone number by mistake, or you didn't check the caller ID carefully before answering, which led to the wrong number. In this case, you may just accidentally answer the phone and then hang up.
2. Telemarketing: Some companies will use the automatic dialing system for telemarketing. If you answer this call, you may find that there is no relevant demand after answering it, so you hang up.
3. Fraudulent phone calls: A phone that starts with 9 may be a fraudulent phone call. This kind of phone call usually induces you to provide personal or financial information in some way, or directly asks you for money. If you suspect that the phone is fraudulent, it is recommended to hang up immediately and report it to the relevant departments.
4. International call: A call starting with 9 may be an international call. If you don't expect an international call, you may hang up because of misunderstanding or strangeness after answering it.
In short, no matter why you hang up the phone starting with 9, it is recommended not to provide personal information or financial information without verification, in case of fraud or other adverse consequences. At the same time, you can also set up an interception list or contact the operator to avoid receiving such phone calls.