Why I can not send text message to any new number through my mobile Samsung S3 mini?

[AC Question]

I'm using S3 mini for last 15 months. I used to send text message as my requirement.
But for last 1 month I couldn't send any text message to any new number which are not present in the current thread.
Also I'm not receiving any text message from any new number........

Plz help me out.

Thanks in advance......

Chinmoy
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