Apple Watch won’t load cellular plan

Help.  I purchased two apple watches for my kids under my first net account.  One of the watches works fine, the second watch will not load the cellular plan that I purchased. I was on the phone for three hours total today between speaking to customer service rep, and tech-support with both AT&T and first net, and the end of the day speaking to Apple. No one can figure out what’s wrong and how to get the dang watch to work. AT&T claims everything looks “perfect quote on their end. I went into an actual AT&T store, and the representative cannot help me at all. I’m being told different information between the 14 people I spoke to you today. Has anyone had this happen to them before?