Three boxes not working would certainly point to something about your network in spite of what Frontier is telling you. "None are receiving a signal"? Can you explain that further? When you scan for networks from Settings->Network->Set up connection none appear or only yours doesn't appear? Can you connect one to your router with an Ethernet cable and set it up for a wired connection to see what happens?
"My account is up to date and paid as agreed." - this doesn't really mean anything. There's no such thing as "Roku service" that one would have to pay for to get a Roku device to work. There's plenty of paid subscriptions for various content, but you don't even need a payment method attached to your account to access plenty of free content.
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