I am not kidding you here but even when I have a full 3G signal which is rare! the speeds are no more than 2G and when things are bad and often they are it's no more than 1.5G maybe even slower.
I am very aware that EE offer Virgin Mobile next to no network, and with BT a major rival in charge of that bit of network that is offered will be squeezed even further, and I have noticed a change since BT took over, it has gone much slower than before.
The contract ends in 2018 with EE what I would do in Virgin mobile's case is get out now or loose a big amount of your already small subscriber base.
Your customer service advisors are liars, they told me that VIrgin was to become a proper network and have its own masts, I looked into these claims made by two advisors and Liberty Global told me "Their was no plans to change from being an MVNO"