Why do my parents owe more on their house than what they bought it for?

Hello, I recently became in charge of my parents’ finances after some medical events. My parents purchased their house in Ontario in 2007 for ~350,000$. They have been paying ~2,500$ a month every month for the past 14 years, and yet now, their debt on the mortgage is currently ~500,000$.How can this be? I know the value of the property went up, but shouldn’t they only have to pay what they originally bought it for?I know that they switched lenders from RBC to BMO a few years ago (Unfortunately, they don’t remember when or why) but would that have made their debt that much higher? They’ve never re-financed or been late on a payment.Any insight would be much appreciated! via /r/PersonalFinanceCanada https://ift.tt/3A0jnxQ