Sony Experia Z3, 200 minutes, 3000 texts, 1Gig data. Contract started January 2015. Just spoke to a phone helper guy who stated that it was impossible to increase my data allowance, but they were able to "award me" an extra 1G to take me to the end of the plan month on the 12th October. I was helpfully informed that I could opt for a higher allowance when my upgrade comes thru in December. Now one of the things that made me use virgin in the first place was their "flexible plan" that I could change once a month... So much for that then
It looks like there is no upgrade option as they have changed the contract packages and removed any alternatives, I'd try again and choose the option to end contact and see if retention are willing to help you
The extra 1Gig will see me through rest of month, I will just turn off mobile data for most apps and go to end of contract but as I'm perfectly happy with my phone, I'll likely go for a BT SIM only contract for a while after that.