I was having issues with my OpenSprinkler getting the correct information from Wunderground when it was going through my firewall. I started getting the notifications from Wunderground saying I had exceeded my limits as well and the Sunrise/Sunset time was incorrect as well on the controller. Everything worked fine when I turned anything off on the firewall that scanned the traffic. Once I turned on anything(content filter, A/V scanner, ect…) that scanned the traffic the OpenSprinkler wouldn’t communicate properly with Wunderground and the calls to Wunderground would go up.
I ended up also posting for help in the forum’s used by my firewall and basically it came down to putting a bypass rule in for the OpenSprinkler. The bypass rule told the firewall to ignore all the traffic coming from or going to the OpenSprinkler. Once the bypass rules were in place everything worked and has been working since. Maybe something to try on your firewall as well.
This is the thread I started about it: https://opensprinkler.com/forums/topic/exceeding-wunderground-api-calls/