SyncUp app not working with watch

Our watch has been dropping calls and not receiving texts for several weeks. We factory reset it last weekend (that didn't help) per a T-Mobile rep and opened the app to add grandparents back as contacts today, but app won't open and says, "All items core API failing." Spoke with a T-Mobile rep, who said this started today, and was told to check back in this thread for an update. It's very frustrating to pay for a device that doesn't even work. We got this for peace of mind when our child goes to a friend's house or has a sleepover, so they can contact us if something makes them uncomfortable or they want to come home. I am seriously considering moving to a different carrier (Verizon has the same watch, and it works WAY better on their network, check out the reviews). We've also been having problems with our phones working (not sending or receiving texts and phone calls). We spent HOURS on the phone the past couple of weeks with one rep saying they would send us a signal booster, and then when nothing showed up in the mail, and we called, that rep said they don't give out signal boosters. My kid's watch not working is the final straw for us. Get it together, T-Mobile!