Complaint Review: North Carolina Turnpike Authority

I accidentally took a wrong turn unto this toll road, got right back off, then received a bill for .96 cents, which I mailed a check a week after I got the bill, next month I recieved another bill for 6.96, the next 11.96 for lates charges. I called them and stated I paid the bill a week after and I sent it in and had proof with a banking statement. They stated I was 2 days late, I assume they processeed it too slow and now scamming me for even more money?