What should I do about a vow to donate five hundred Riyals every time I return to a specific sin, knowing that I have not yet donated and do not know the number of times I have broken the vow?

If the intention of the vow is to prevent oneself from doing something, then it is considered an oath, and the one who makes the vow has the choice, if he breaks it, between fulfilling the vow or offering expiation for breaking an oath. The expiation for breaking an oath is feeding ten poor persons, or clothing them, or freeing a slave. If he cannot find any of these, then it is fasting for three consecutive days. It is preferable for a Muslim to abstain from sin without a vow or an oath.