Why does Apple's mobile phone often receive a number starting with 000?

Because strange numbers are not blocked.

You can turn off iMessage in the settings of Apple's mobile phone, or turn on filtering unknown senders in the information in the settings to turn on SMS filtering.

There is no area code with three zeros in succession like 000. Generally speaking, a 0 call is a domestic call and two 00 calls are international calls. If the caller ID of the phone you receive does start with 000 or more zeros, this may be a problem caused by multiple telecom operators switching networks.