how many of the 12 fibres are being used?

if they've installed a 12 strand and are only using two, you could up the datarate by using several fibres. This would easily speed up your connection to near gigabit. (12 strands giving 6 circuits, each running at 100Mbps duplex. 1.2gbps) .Hardware may not be cheap, but certainly cheaper than running a new single mode fibre and buying new hardware.