cell phone says internet connection too slow to connect

I am going through my Verizon data quickly and expensively. My phone and my families phones keep saying internet connection too slow to connect.  Tried changing out on two different routers fairly new Asus Black Knight router is what we use. Still having issues 

4-6 times a day I get this message. Laptops having issues and one Roku too but funny thing is one Roku has no problem. Ever.

Did all the checks with direct plug in using laptop and no issues but then again it is for like a minute or two on and off. Longest time was 15 minutes and when I plugged in, it was fine. 

Often times now the laptops are all saying limited connection.

My brother is IT and checked out my laptop and it was fine , adapter etc so he checked router but it too was fine. He says cox has had issues with packets showing downloading but actually no info coming in. He has talked to techs that come out and they understand his lingo on what issue was but still not fixed. He lives across street from me. I need to get the exact lingo from him and post here. Will do so when I can. Something about new hardware they installed that is defective.