Several years ago I invested in a company where they deal with interest. Unfortunately, some of the profits that I got were also as result of their investment with interest. I tried to find out the exact amount I got so that I remove them from my original investment, but it seems very, very difficult. What should I do? I have repented to Allah to forgive me, but I still feel very guilty about it. Please advice! May Allah reward you the Janna without reckoning.

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

If a Muslim earns forbidden money, he is obliged to get rid of that money by spending it in useful ways, without using even a small amount for himself. If he cannot decide the amount that he wants to get rid of it due to forgetfulness or mistake, he should act according to his strong assumption about the amount, and then should get rid of it. For example, if he strongly believes that the amount he wants to get rid of it is 700 Dollars then he should do so. He will no longer be considered sinner since he did what he could do. Allah does not burden one beyond his capability. The amount he sets apart maybe less than the actual amount he should get rid of due to his inability to calculate it, but the Shari'a only demands that he act according to his strongest assumption.
Allah knows best.