we have a water leak but cannot find it.it only shows on the meter when you turn on a tap.?

your question, is confusing

there is no leak when all the taps are off,

but you say the seller, [cellar] is filling up?

and the pump is pumping it out ?

and that's normal in the winter, ? but not in the middle of dec,

suggestion, rethink what your saying,

nothing makes sense,

Sounds like you may a Wet Spring. These springs are dormant during dry conditions; but during wet conditions the water level will rise. I had one under a house I use to own.

If you have the faucets turned off and the meter isn't turning, there is no leak.