You cooked them too long....you now have "hard candy"...are they hard enough so that it will crack like toffee?
Linda C

They can't be softened. The only options are to give to someone who likes hard candy or crush/grind to make crumbs and use them as topping for ice cream desserts, cakes, etc.

You might want to calibrate your thermometer. It only needs to be off a little to create big problems with candy.

Carol

Could they be simmered with some 1/2 & 1/2 til melted for an ice cream syrup?

When you poured the caramel into the pan, did you scrape the pan? The scraped stuff can also be harder than what pours out & will harden the caramel more.