Hi there, @Nuopuda. Welcome to the Lucky Mobile Community, and thanks for your post.
To confirm, are you sending pictures and/or videos, otherwise known as MMS, via your text messaging app of choice? It's important to note that this does count as using data as opposed to traditional SMS.
Alternatively, are you using a third party messaging app such as WhatsApp? Depending on how you have it set up, these would be defaulting to instant messages and not SMS, thus incurring data usage.
Let us know if you have any further questions. Best wishes.
