Is there a sin or transgression in applying for a government housing unit whose value and installments have doubled, with a profit exceeding one million, and is continuing with the installments considered participation in usury, and what should be done in this situation?

If the price of houses offered by the government is an estimate, and then it becomes clear at the time of contracting that the actual price is higher, with the possibility of increasing the price by extending the installment periods, there is no harm in that if both parties agree upon a known price and specified periods at the contracting session, because time has a share in the price, and the important thing is to agree on one known price. However, if something else is intended, please clarify.