Wifi problems for iPhone 4

I am having trouble getting my iPhone to connect to the wifi in my house. I began downloading an app last night and once I realized how large it was I didn't want it anymore. I read a couple of blog posts that instructed to fool around with airplane mode/turning off wifi in order to cancel the download. Not only did it not cancel the download but now I'm having trouble connecting to my household wifi. I erased the network from the phone and then rejoined but that did not solve the problem. I brought it to an Apple store and I was able to connect to the store wifi and the guys at the Genius Bar fooled around with my phone and I thought it was finally fixed. As soon as I got home I was back on 3G. My macbook is running off of the house wifi so I know it's not a matter of signal strength. I restored my phone but that did not help. Now whenever I turn the 3G off my phone looks like it's running on wifi but it won't connect to the internet or transfer data. When I rejoin my wifi network the wifi icon appears for about 10 seconds and then reverts back to 3G. Does anybody have any similar issues or suggestions on how to overcome this problem? I appreciate any and all help. Thanks.