Is it permissible to replace a defective gold bracelet or to get its price back if the seller refuses to refund the money, claiming it would constitute usury due to the change in the price of gold?

If he buys gold and finds a defect in it, he has the right to return it and reclaim its price. He may also leave the price with the seller and then buy other gold with it, because iqalah (rescission of a sale) does not require immediate possession of the counter-values. Similarly, he may exchange the money owed to him by the seller for gold, taking gold at the exchange rate of the day, provided that they part ways with nothing remaining between them, based on the hadith of Ibn Umar (may Allah be pleased with both of them). This is what permits buying gold with money that is a debt owed by the seller.