Mine hangs so that they reach up to drink. Took them several hours to figure it out. Maybe click the nipples so they have drips hanging from them so they find it when they start looking for something to drink. Then it's best to walk away or you'll go crazy worrying

Did you hang it in the same place where the water used to be?
Also, from what I understand, the vertical nipples will freeze even if the bucket has a heater in it. I use horizontal nipples on my heated buckets. These have an o-ring so they don't have water inside them like the vertical ones do.
Good luck, I hope they figure it out soon!