Specially if you broke a promise you should obey this ayat.
Allah will not impose blame upon you for what is meaningless in your
oaths, but He will impose blame upon you for [breaking] what you
intended of oaths. So its expiation is the feeding of ten needy people
from the average of that which you feed your [own] families or
clothing them or the freeing of a slave. But whoever cannot find [or
afford it] - then a fast of three days [is required]. That is the
expiation for oaths when you have sworn. But guard your oaths. Thus
does Allah make clear to you His verses that you may be grateful.
The intention that you have in your hearth when you do that surely matters according to the follow ayat. (Specially Allah, and you, know better than us the severity of the potentially commited shirk)
Allah will not call you to account for thoughtlessness in your oaths,
but for the intention in your hearts; and He is Oft-forgiving, Most
Fear Allah, follow His teachings, and I hope He will forgive you.