Answered by Ustadha Umm Abdullah
Salam. I have a question. Previously i.made a promise to Allah swt if I was to get better health wise then I would never do a certain sin again ( which detiriates my health). However once I got better i fell back in to that sin. I read in surah tawbah verse 75 which seems like a familiar situation to mine. In that case Allah set punished them with hypocrisy. I only had one chance as I committed the sin then I failed on my promise. Whereas they could pay charity and change anytime. But because they rejected Allah swt punished them. What shall I do? Will I be able to repent for this?
In the Name of Allah, the Most Gracious, the Most Merciful.
If a person made an oath using the following expressions, “I swear by Allah”, “By Allah I will not do this”, or “I make this action haram upon myself” and then broke the oath, he will be liable to pay kaffarah. 
Although one may have broken his oath, he should not be despondent of the mercy of Allah. Consider the following verse where Allah Ta’ala says:
“Say, Oh my bondsmen(servants)who have wronged their souls, never lose hope ofAllah’s mercy. Verily, Allah forgives all sins. Undoubtedly, He is the Most Forgiving, the Most Merciful”
[Surah Zumar: 53]
From the above verse, one can deduce that well before death arrives, the repentance made from sins, no matter how serious, even from kufr (disbelief) and shirk (ascribing partners to Allah Ta’ala, gets to be accepted. By virtue of a genuine taubah (repentance), all sins will be forgiven; therefore, none should lose hope in the mercy of Allah Ta’ala. (Ma’arifulQur’aan v7/p574)
Only Allah Ta’ala knows best
Ustadha Umm Abdullah
Checked and approved by Mufti Mohammed Tosir Miah
رد المحتار علي الدر المختار ج ٣/ص٧٠٧