PC and Cell Drop no connection random

[rookie1]

We are Desperate to find a solution

Everything used to works fine for year ..suddendly we lose internet intermitently on the devices

Some devices seem to work for a while, while other stop

We use Cable (PC) and WI-Fi (PC and Cells)

We changed the router but was worst result so we came back to the previous router.

We Diconnected all PC cables to the routers and reconnect one by one to test if one of them was the problem ..no good results

Speed Test show to everyone a MAX speed OK

Videotron provider says by long distance test that their Modem was OK.

We unpluged wireless phones ,Printers, no good results

We are in a home not a apts Buildings

What else Could it Be ???

Can neighbours make our connections dropped??

Anything you can think of ? Like I said everything was Fine for years and then suddendly This happend :(

Thanks guys for your time :)