Chase Card increase from 8.99% to 29.99%

I recently had a rate increase on my Chase Card that I have had for years. I had to attend to a family emergency on the East Coast a couple of months ago and missed my payment by 4 days. This was the first late payment in years of having the card. My rate went from 8.99% to 29.99%. I called the 800 number on the bill to dispute and the person hung up on me. I went into my local Chase branch and the manager was able to remove the late fee but nothing else. I don't feel a 21% rate increase is justifiable. I have been loyal to Chase for years and don't appreciate the slap in the face received by this ridiculous increase.