Incorrect password for wifi?

I recently moved into an apartment, and we got our internet installed this month. My iPhone will not connect to our wifi. Whenever I enter the password, it just says: "incorrect password" even though I have entered it correctly over and over again.

I have done multiple things to see if I could fix this problem:

I have entered the Gateway address into the URL on my browser and then gone into the router settings and changed the WEP to OPEN.

I made sure my iPhone was up to date.

I cleared all cookies and history in Safari.

I made sure my cellular data was turned off.

I turned airplane mode on and off.

I tried entering all the codes on my modem into the password bar.

I don't know what to do now. It still says incorrect password. It doesn't even seem to TRY to see if it's a correct password, it just seems to know immediently and without even waiting a second, the error pops up. What do I do?

-Noelle

As an additional side note: There are 3 laptops in use, all of which can connect to the wifi as well as some game consoles.