Cancelled Cox Internet service.

After 20 years with Cox I had to cancel my Internet Service to my Home.
I do not have any equipment or other services from Cox.
I cancelled well in advance prior to my next bill.

When I started with COX I paid a full month when they started my service.
So actually I pay ahead of my service month.

Now they say they don't get paid in advance but after the month is up and want me to pay another month for internet service from them

Am I missing something here?
Do I need to have an Audit for the past 20 years to prove my point?

What do you think?
Thank you