Home wifi keeps switching to public hotspot

My home internet keeps switching & connecting to a local xfinitywifi hotspot, and won't stay on my home network even tho my pigging & chromebook indicate my connection strong! I notice it's happened again whenever my webpage or video suddenly won't load, or the "spinning wheel of death" appears when something is loading ... (ie, when the connection speed suddenly drops  so much slower than my home wifi). I've done the requisite turn off-on/restart, unplug-plug back, "forget" & re-add network, ensured my chromebook & phone are up to date, etc etc... too many times to count, so NO!  i just WON'T do it any more! And the live chat helpers have to go thru the same [Edited: "Language"] script every single time ("turn off your modem... wait 10 mins... are all the lights on?... it's one blinking?..." augh!!!). And when they can't fix it, I get passed on to a supposed next level supervisor, who then uses the same [Edited: "Language"] script... it's beyond frustrating. 

The chat bot & live tech support NEVER fix anything & they always just give up on me when they reach the end of their script. 

Something else is the problem & I'm just not tech savvy enough to fix it myself.  

And yes,  I've checked my wifi & various app settings (on all devices) & given permissions,  etc, but eventually even that route brings me into the bowels of the devices that only someone with real tech capabilities should go.  

Help? Before I pull all my hair out?