I would be worried that your trouble has nothing to do with your internet provider, and everything to do with some fault in your network. Especially as the trouble has remained the same despite the switch from one carrier to another.
I would suggest that you might want to identify that the trouble is in fact your ISP before switching again.
We use a piece of hardware and a software subscription to monitor and track troubles like these on our projects. It may be that the cost is low enough, and the procedure simple enough, that you might be interested in doing the same. Or, you might want to hire a professional to do it for you. The lowest cost IP monitoring service I know of is Domotz,
www.domotz.com. A few weeks with a Domotz device connected and you should have enough info to diagnose your trouble.
That said, I may have a free solution. Sonos runs an extremely competent support department, and one of the things a Sonos system does is log the network activity and behavior of your home's connection. If you were to place a support call to Sonos, and describe this trouble, there is a very good chance that they could point you in the right direction.
There is another reason I mention Sonos. An incorrectly installed Sonos system can actually cause the types of problems you describe. Sonos systems actually build a parallel network, along side the network already installed in your home, and the Sonos system itself decides how it should send its traffic. Sometimes they use your hardware, sometimes they use theirs, most times they use a bit of both. Because of this topology, there is a chance that the two can interfere, and cause spurious trouble like you describe.