As I look at the site now you have mulitple viewport tags. Try removing them all and replacing them with either
<meta name="viewport" content="width=device-width, initial-scale=1.0">
or if you want to prevent user zooming:
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=0">
UPDATE
Also, in you media queries you use max-device-width, e.g.
@media only screen and (max-device-width: 760px) {
...
}
Unless you are trying to target specific devices, you could try just
@media only screen and (max-width: 760px) {
...
}
Device width and width aren't the same thing and for responsive design, width will usually get the results you want. This link has some more background info about the differences
Hope this helps!