Lumia 1320 :: How To Get WiFi To Override Data When In Range Of Wireless Connections

I switched to Cricket from Virgin Mobile so I could go back to Windows with the 1320. In my 1st month with them I went over my 2.5 GB of data with about a week left in the month. In five years with VM I can count on one hand the times I went over 1.5 GB with them. Checking my data usage on Cricket's website I see 1-3 entries per day detailing my usage, some with very large amounts of data. Cricket CS tells me that my device uses their network first and Wi-Fi 2nd.

So in other words when I'm at home and connected to my home wi-fi the device will use Cricket's data even though it's connected to my Wifi. To fix this they told me I have to manually disable data from their network when I don't want to use it. Now this makes no sense to me since the 3 Android phones I've had did not do this once I connected to Wi-Fi the carrier's data was disabled. I think there must be a setting on the phone that must wrong that is keeping this from happening other that what Cricket CS told me. The way they explained it to me Wi-fi is useless because their data would be used regardless if it's connect or not.