I am sorry for the loss of your tank inhabitants!!
As RLee said, failures do occur with all equipment at some time and everyone has a brand that they won't ever use again because of some failure.
On a side note, I always under-size my heaters in the event of a heater failing in the ON position to help minimize your horrible experience.
Eheim Pimpette #270
Eheim Pro II 2028; Classics Series -2215, 2217, 2260, 2262; Pro 2229 Wet/Dry