But their principal balance jumped $43,000 to $260,000, and their mortgage payments grew by $30 a month.
Their principal balanced increased by $217,000 and their mortgage payments increased as well. 
mnli hypothesis: Their principal balanced increased by $217,000 and their mortgage payments increased as well.  premise: But their principal balance jumped $43,000 to $260,000, and their mortgage payments grew by $30 a month.