My wifi has slowed down? Our iPads and iPhones take a long time to connect using WIFI?

My wifi has slowed down? Our iPads and iPhones take a long time to connect using WIFI? I have a wifi extender and it is the one that we are having trouble with-I think. About a week ago I talked with the extenders support people for an hour and reset everything in the "Network" Systems Preferences. Worked great until now.

Why we are mainly trying to do is check our email at breakfast and in the evening do streaming video. It used to work just fine, most of the time. There was only intermittent slow/stopped wifi signal connections at that time.

Now when trying to watch one episode of something from any of the Streaming networks we have this trouble. Networks being Netflix, Hulu, and Amazon Prime.

Am I going to have to call the support people at the network extenders company? I know that it is one suggestion, even my spouse suggested it.