How far are you from the exchange, what is your contention ratio? All things to consider. I have 8mb bb here and it runs at
Downstream 2,597.1 Kbps ( = 2.5 Mbps )
Upstream 377.3 Kbps ( = 0.4 Mbps )
and the exchange is just down the road from me. 8mb is the maximum. What you get varies depending on who else is using the connection, how far you are away and the quality of the line.
So count yourself lucky to get what you do. Moving service may just end up getting you the same thing if it is factors outside your control such as line quality and distance from the exchange.