I'm paying the fixed monthly price I negotiated 20 years ago, back when my house was worth a fraction of what it is currently worth.
A nitpick: no you aren't, unless you don't have property tax and homeowners insurance in escrow paid out of your mortgage payment. I bought a house in 2010, thanks to the 2008 economic crash I picked it up for $43k on a FMV of 90k. I was young and had a low wage job at the time so I went for a 30 year mortgage instead of 15, and my payment with escrow was only $386/month. Fast forward to last year when I sold it, my payment at that point was nearly $600/month due to taxes and insurance both nearly doubling.
Also fun fact, even though I sold it for nearly three times what I "paid" for it, I didn't profit nearly as much as you'd think due to that massive amount of interest I paid over the 15 years of a 30 year mortgage. If I had taken the 15 year loan it would have been paid off for six months before I sold it, and in fact I probably wouldn't have sold it. When you're in your 30s, 30 years doesn't seem much longer than 15. If I bought a house today I would go for 15 years...not that I can afford to buy one today. I'm lucky that I live in an inherited house now but most people don't have that going for them.