I just now fixed my Samsung, which had the same problem. The drum would not stop spinning - even after the control panel was turned "off".

Apparently the problem was that the "fluff" mode, or "wrinkle free" mode had been activated and needed to complete its full cycle. Turning off the machine, or even unplugging it would not interrupt the "fluff" mode. Apparently Samsung takes its wrinkles VERY seriously!

To "fix" it, I turned the fluff cycle to the lowest possible time and just let it finish its cycle. I suppose the cycle might have run its course if I let it go the full regular time, but that is 3 hours! Anyway, the dryer works fine now.

Good luck with yours.