Answer
(Fatwa: 123/124=D/1429)
If the husband admits that he sent the SMS of talaq, then the talaq shall take place. And, talaq once pronounced or written cannot be taken back. But, if the husband writes the abovementioned words only once, then only one revocable talaq took place in which he can take her back in his Nikah. So, you should clarify what was the wording of SMS and how many times he wrote it. And, what was the wording of first talaq and when did he give it? And, what does he mean by his words: “I give second Talaaq to you and if you again send an SMS you know our marriage will be over.? And, did you send any SMS after this of him or not?
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband