Shop employee selling goods on his own account from his own wealth – what should he do now?
Question

I used to work in a shop when I was seventeen years old. This shop used to buy phonecards for 10 pounds and sell them for 15. When the shop ran out of cards one time, I told the owner of the shop to bring more cards, but he did not bring them, so I bought them with my own money, and I kept the profit for myself. When I left that job a few years later, my conscience stirred and I said: I must return the profit to the shop. So I left him 150 pounds when I left the shop, and I donated 140 pounds in charity in the name of the shop owner. My question is: I still have 300 pounds. Should I send it to him at the address of the shop, or should I give it in charity in his name? Please note that the owner of the shop goes to extremes in committing sins, so I do not know what he will use the money for. How much should I give him, when I do not know how much the profit was? Moreover, the value of the pound has dropped, and what I am talking about happened approximately 10 years ago. May Allah bless you and those who are doing this work.
Praise be to Allah.It is not permissible for a worker in the shop to sell anything on his own account and keep the profits for himself, because this is a betrayal of trust and is deceiving the owner of the shop. We praise Allah, may He be exalted, for guiding and enabling you to repent and ask what you should do now.
You must return to the owner of the shop the profits on the cards that you sold, and you should strive hard to work out how much these profits were, based on what you think is most likely to be the case, so that you can absolve yourself.
With regard to the amount that you say you left in the shop – which is 150 pounds – if you intended it to be compensation for the amount that you earned, then you can deduct that from the total amount that you owe.
With regard to the amount that you gave in charity on behalf of the owner of the shop – which is 140 pounds – you do not have the right to deduct it from the total amount that you earned, which is now a debt that you owe, because what you are required to do is return the money to its owner, not give it in charity on his behalf.  It is only permissible for you to do that if you have lost contact with this man. But since you know where he is, you do not have the right to give anything that you owe in charity on behalf of the one to whom you owe it.
You should understand that this charity will be regarded as having been given on your own behalf, if Allah wills, and we pray to Allah that you will find it in the balance of your good deeds.
You have to work out what remains due to the shop owner and send it to him: in order for your repentance to be valid and acceptable, if Allah wills.
The changes in the exchange rate from what they were at that time do not affect you. All you have to do is to return the money that you took from the profits, without any increase.
We ask Allah, may He be exalted, to accept your repentance.
And Allah knows best.