You don't qualify for Seasonal Hold because you sold your house. Seasonal Hold assumes you're still living at your current address. Meaning, you'll eventually return to the address, continue the same service and resume paying your bill.
If you sold your house without transferring your Cox service to a new address, you basically canceled your service. However, if you pay via EasyPay, I'm sure Cox will gladly keep fully charging you until you return their equipment.
If you cancel your service, Cox will keep your email account active for 90 for you to create a new account. Use this time at your son's house to transfer your email service to another provider. This stinks but you're essentially homeless and you can't have Cox service without a house.
Where are your cable-box, telephone modem and, if applicable, Panoramic router?