I didn't do broadband but received a text message.

If you haven't applied for this mobile phone card, then this message may have been sent by mistake or someone else used your ID number to apply for a mobile phone card.

In order to confirm this, you can call the customer service phone of China Mobile and provide your ID number to the customer service staff to find out if anyone else has used your ID number to handle calling cards.

If you confirm that you haven't handled this mobile phone card, I suggest you contact China Mobile Customer Service in time and ask them to verify the source and accuracy of this information to avoid possible security risks.