How to setup proxy

Good Morning

I bought a Multitech Conduit AEP gateway a year ago. In my house it works perfectly but in the office we have a FORTINET proxy.

I do not know how to make the gateway connect to the internet. x, y, z and t are values for a local IP. I have tried with:

ifconfig eth0 x.y.z.t netmask 255.255.255.0
route add default gw x.y.z.1

export http_proxy=http://user:pass@x.y.102.1:1000
export https_proxy=https://user:pass@x.y.102.1:1000

ping http://www.google.com

But it doesnt work. What can i do? The firmware version is 1.7.3

Thanks!