Trial subscription expired 5 days early

Popup box came up that said I had turned off my antivirus. I looked at the Norton interface and it said my subscription had expired. However, when I got on Google the Norton Safe Web service appeared to still be working. I couldn’t find a number to call or any info for my problem on the Norton site so I went ahead and renewed. I was going to anyway but it’s very agitating to suddenly have this happen early and be online on Yahoo and Twitter already when I was informed that I had no antivirus protection. Any idea why this happened?