They didn't confirm if the router would or wouldn't be charged for after the contract expires but for the first time I am going to advise him to cancel his DD once the switch is done because I don't trust this company.
Don't do that.
If the provider tries to collect money and fail, they will treat this as a debt and may pass it onto a debt collection agency, causing massive aggrevation and rapidly spiralling costs, not to mention a black mark on the credit file.
* Ride out the contract to the end
* Return the router, if that's what the contract says you have to do. Send it signed-for so there is proof of delivery. Do this at your own expense - it's worth it.
* Pay the final bill.
* Once this is completed and they've confirmed nothing more is due, cancel the DD
* If you are in dispute about the final bill (e.g. you disagree with a charge they have raised, like charging for the router even though it has been returned) then pay it and raise a formal dispute. Take it to a small claims court if necessary. These often side with the consumer.
* Keep written records of all correspondence and phone calls to back up your case.
Note that some providers do charge an exit fee if you cease the line without transferring it to another provider. It will be in the T&Cs.