ᐅ Cistern Always Empty Despite Rain

Hello,
I hope I’m asking in the right place.
We have a problem with our newly built house: our 7000-liter (about 1850-gallon) cistern is always empty.
Even after two days of rain, there is so little water inside that the pump can’t push it up.
Considering the pitched roof has an area of 200m² (about 2150 sq ft), it should collect a significant amount of rainwater.
Our neighbors with cisterns all have water.
Where could the water be going?
If the downspouts were clogged, they would overflow.
The cistern is made of concrete and was installed as one single piece.
What ideas do you have?
Where could the problem be?

You don’t have that many options. Check the supply line.

Has it been tested whether the cistern is watertight?

Either nothing flows in, or whatever flows in flows back out.
Tip the watering can into the gutter and catch the water again in the cistern to compare.

I would also tend to say that your concrete cistern has some kind of defect. If it rains for two days, there should be enough water in it for the pump to work, especially with a 200sqm (2,150 sq ft) roof area. But as already mentioned, pour water in at the top with a watering can and check at the bottom if roughly the same amount comes out.

We will get started on this today.
I am not sure if the airtightness has been tested.
First of all, thank you very much for the help.