Hi,
I doubt they have
taken 2MB away from you when the companies merged, as per the
Virgin Media website you can see that your 4MB connection is still offered by the company, they have just renamed it to Broadband Size: L. Whereas the 2MB connections is Size: M.
Check your modems config file by going to 192.168.100.1 from Internet Explorer, suggest not using another browser as my Modem doesn't like any browser but Internet Explorer.
Post the Downstream and Upstream rates here, and we might be able to help you out further, also check a recent bill to see how much your paying and compare it to the price of the services on the website above.
Thanks, Andrew Robinson.