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 is His slave and Messenger.
We answer your question with the fatwa that Shaykh Ibn ‘Uthaymeen issued to a questioner who asked him about the ruling of eating from the food of his brother who works in an interest-based bank, and he answered, "There is no sin on you, even if you believe that it is haraam (unlawful), because it is proven that the Prophet ate from the food of the Jews, and the Jews – as you know – consume what is forbidden and take interest, and the Prophet did not ask them, 'Did you deal with interest or not?' This is evidence that it is permissible for a person to eat the food of someone whose earnings are unlawful, and there is no sin on him…"
There is no limit that a person should not exceed, like one meal or two meals and so on; rather, he may benefit from what is spent on him, and the sin falls on the one who earned the unlawful money, and not on the user (who ate the food).
So you should avoid these obsessive whispers and not get carried away with them, otherwise this will spoil your religion and your worldly affairs.
Allah knows best.