Do you wait until the end of the billing cycle to cancel service?

I canceled cable service 9 days ago and received a confirmation number. After this month, I am not paying any more ATT cable bills. Do you all wait until the end of the billing cycle to cancel service? I am not paying for cable service after March 12 when I called to cancel. I’ve tried to reach a representative over the phone and chat with no luck. I do not want any special offers. Please cancel the cable and keep the internet as I stated nine days ago.