Why isn't my Internet working on my iPhone?

Its been going on for around 2 months now, and my Internet won't work! It only works on 3G (which costs money). I reseted the network thing, turned it to airplane mode then back to the internet etc.
It still won't work for some reason.

----------------------------
My iPhone is an 4s
iOS is 7.0.4
Other internets work, but not this one that I mainly use.

Have you checked you've inputted the right password? It sounds stupid but its worth a check.
if not go to an apple store

I'm guessing you are useing Wi-Fi?
Make sure the Wi-Fi is on and go into there and choose the forget network option
Settings>Wi-fi>select the network>select "Forget this Network", then try reconnecting making sure you have the right password and not too far from the hotspot/router.
Use a laptop, tablet or another device to also connect to the network to see if it gets internet, if not your router or modem may not be connecting to your ISP, unplug both of them and wait little, about 5 mins and re connect.
Wait a min or two for it to connect to the network and try again.
Still unable to connect contact your ISP (time Warner, comcast, att, etc)