I don't know a lot about the wifi service other than your complaint is not unheard of.   The GS3 is a fast phone and will connect to the best service.  Your home wifi service may be over taxed by many devices at once, or needs a firmware update, or has a problem.  

I have upgraded cable internet and am glad for it, dial up or fois is horribly slow in comparison.

I suggest complaint to customer service, we here at Forums can only validate your concern.