My phone is a samsung galaxy s3. I have a data plan but use my home wifi when available. Almost every month at some point my phone will switch from my home wifi to my data plan without my knowing and it eats up my data. I looked through the usage and you can see the random spike in usage as well as it seems that everytime it happens its youtube. I have been on youtube before and it uses wifi but once a month it will use the data instead. I have no idea how to fix it from doing this and am getting frustrsted that I get a week of data before it gets used up for no reason. For the next 3 weeks I have no data now. I wont waste my time trying to get it refunded but I just want it to stop happening. Icant afford to spend money on a data plan that I never get to use.