Just ask the dealer to disconnect the modem upon purchase.
Better yet, refuse to buy shit you don’t own and make this known. Go to the dealer force them to stand around while you read the privacy agreement. Use an attorney because they have stupid legal agreements. Waste everyone’s time because they are the ones doing this to you. It must cost profit. Then walk away from this bullshit. Tell them why you are walking away.
All of this exists because people are too stupid to care. If you ignore this, you are one of them, and part of the problem. Legal agreements are theft and slavery. Signing them blindly is the stupidest thing you can ever do in your life. Anyone that needs a legal agreement for you to make a purchase is a worthless criminal. Signing their bullshit is saying you are okay with being their little slave bitch.