Send a short message to Unicom with a mobile number, and as a result, the number of another telecom has also been received. What's going on here?

Because the mobile phone number at the beginning of China Unicom 133 has already been transferred to China Telecom as a whole, and China Telecom has tied the original customer's number with the mobile phone number at the beginning of 133 transferred by China Unicom, so the situation you mentioned appears.

I sent a short message to Unicom with my mobile phone number, and I received the number of another telecom.