Cannot find wifi on my iphone 4s

I recently swapped my phone out for the 4th time at my local apple store for the hearing speaker going out on me......and now the newest one which I got less then 20 hrs ago has no idea what wifi is....In the store it had trouble finding it, and as of 2 hours ago it no longer can find wifi in my house while 4 more iphones and an ipad have no problem