There have been bank messages in my husband's mobile phone, but I have never seen that card.

There are two possibilities for what you said. First, your husband has another card that you haven't seen or told you. Second, his mobile phone number was registered by others before, and others have never used it or cancelled it. Later, your husband bought this phone card, so he will send this message often. If so, you can apply to the bank counter for the staff to help your husband cancel the original SMS service.