Dispute my Digital Life billing

I recently received a call from Digital Life after I paid my account off in full and canceled it. The representative stated that I was charged because I didn't cancel it until after I had paid it in full. It had been disengaged due to past due payment. Well, I was unhappy with the service so I paid it off in full and canceled it so I don't feel that I owe them a dime. The representative said that my bill is for $53.00. Please help me resolve this as I am no longer a digital life customer and it really jeopardizes my other account with AT&T.

Jonathan [edited for privacy-please do not post personal or unique information such as but not limited to full names, employee ID numbers, email addresses, phone numbers, account numbers, etc.]