Sayyed Mohammad Al-Musawi,
Sayyed Mohammad al-Musawi is originally from Iraq and heads up the World Ahlul Bayt Islamic League in London. Other than being involved in various humanitarian projects, he frequently responds to religious questions. In the past, he has also spent significant time in India guiding the community.
It is obligatory to fulfill the promise to Allah, and if you did not fulfill it, you will be committing a sinful act and there is a Kaffara on you which is either, freeing a slave, or feeding sixty poor persons or fasting two months.
We are not allowed to change our mind after promising Allah.
The Promise should be pronounced verbally and not just in your heart.