For any version of ProxySG or ASG(Advanced Secure Gateway)
You can view Quota usage or Statistics by accessing below URLs :
https://IP_address:port/quota/time/view ( Time Quota)
https://IP_address:port/quota/volume/view (Volume Quota)
One thing to keep in mind that on these URLs, all fields are case sensetive. So you must use exactly same as what you have used in policies on Proxy othewise you won't be able to see correct information.