All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It is due on you, first of all, to repent from that sin with sincere repentance. The conditions of sincere repentance are: regretting what you have done, giving up the sin, resolving not to return to it, and giving back to the company what you have taken illegally, and you will not be free from liability unless this money is given back to its owners. If you fail to do so and rather insist on the sin that you are committing, then your fast is feared to be fruitless and bereft of reward. It is proven in an authentic Hadeeth that the Prophet, sallallaahu ‘alayhi wa sallam, said, “The one who does not give up false speech and acting according to it, Allah is not in need of his abstention from food and drink (i.e. his fast).” Without a doubt, consuming people’s wealth unlawfully is of the falsest deeds.
So you should, dear brother, hasten to make sincere repentance in this blessed season, and keep in mind that Allah is the Most Forgiving, the Most Merciful towards the one who repents and returns to Him, and that His punishment is severe for the one who disobeys His command and persists in sin. So do not expose yourself to the anger of Allah for which neither the heavens nor the earth can tolerate.
As for buying food to break the fast with from that money, without a doubt, it is unlawful. You are the guarantor of this money, and you must return it to those entitled to it, as we have already mentioned. If your fasting was correct, you are not required to repeat it, and this sin does not nullify it. But unless you repent, you may be deprived of its reward and your deed may be fruitless in view of the hadith which we previously mentioned.
Allah knows best.