If a person bought a house not knowing that such a transaction is forbidden, he doesn’t have to sell the house unless he is sure he will not acquire a loss and that the instant payment will decrees the interest which is the forbidden part.
But if the interest is the same whether he pays it immediately or in installments as previously agreed, in this case he shouldn’t sell the house as the damage has been already done and it is only logical to continue to live in it and give them the payments on time.