Heated 3 Gallon Flat Back Bucket

I bought 14 buckets last fall and had to have all of them replaced due to freezing. I now have 4 of 14 that will keep water liquid from top to bottom at all temps. I called mfg to complain and was told to put bucket in freezer for at least an hour then plug it in immediately and listen for a "pen click" as that is the sound of the thermostat resetting. That didn't solve the problem. Clearly the heaters are on as the water is not frozen in the buckets from top to bottom. I just have to break ice off the top 2 or 3 times a day so my goats can get a drink. These are in an insulated barn that is not heated and will drop below 32 as the outside temp drops. I have 5 gallon buckets from different mfg that will keep water thawed at all temps even if sitting outside in freezing weather. Something is awry with this bucket.