When you say "planted"-was this turf or seed and did you stipulate what sort of lawn your wanted?
It may be the type of seed used to produce your lawn is one of the finer types and will only grow so high-or the soil has no nutrient and therefore the grass has nothing to feed on-but the presence of worms would contradict that
The only thing you can do it to commence a feeding programme-with a high nitrogen feed twice this year in the warmer months to produce top growth -then an autumn feed to develop root growth
That should help-don't mow too short-but if it is genetically a short lawn there is not much more you can do.
But you cannot do anything until it warms up a bit and starts growing.
Perhaps contact the people that laid it -was it a professional company-did they offer any sort of guarantee??