Login to network

I have the unlimited plus prepaid plan for 70 bucks. I always pay my bill on time bc it is on auto-pay. It always seems after the bill is paid or around that time, at&t shuts my data completely off for at least 6-8 hours. I am really confused and irritated at why this keeps happening. I don't go over 22 gigs a month bc I thought that was the problem, but it still does it. Any insight would be great.