I have a specific question regarding bank loans. I have looked through all the questions and answers on your site regarding this issue. My parents took a bank loan 21 years ago to buy a house. We live in Europe. However, 21 years later they are still paying since they pay the interest. Practically they have already paid the value of house. It never came across our mind that this was Haram. Or let's say we were focused to get a house because it was more economic and secure than renting. For your information renting an apartment in this country will not leave anything of the salary. And it's also very difficult to find apartments as well. Our major concern is now have we committed a great sin in this issue? Second, should we try to get rid of our house as soon as possible bearing in mind that it's so difficult to find apartments which less cost since they are usually more expensive than houses?

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.
No doubt taking interest-based loans whether they are for purchasing a house or for anything else is forbidden. Know that dealing with Riba is among the major sins. May Allah Protect us from all kind of sins.
Therefore, the one who was involved in such a sin should  sincerely repent to Allah and ask His forgiveness. You are not obliged to sell the house since the house is not Riba (usury/interest) but the Riba is the sum you pay to the bank more than what you have received. Thus, the borrowing person is sinful due to his cooperation in dealing with Riba. Jaabir, may Allah be pleased with him, narrated that the Prophet said “Allah has cursed the one who consumes Riba (i.e. usury or interest), the one who gives it to others, the one who records it and the one who witnesses it (its transaction).” He added: “All of them are equal in sin.” [Muslim]
Allah knows best.