A Unicom number sent me several short messages a day saying that I was using your mobile phone.

If you haven't lost your mobile phone, don't believe such messages easily. At present, there are many SMS scams, and once you reply, you may steal the relevant information in your mobile phone. Be wary of SMS fraud. If it is determined to be fraudulent information, you can also report it to local customer service. If the mobile phone is lost, try to change all business passwords bound to the original mobile phone to avoid losses.