Our water bill has been consistent for nearly 5 years at 30 - 35 euros per quarter. This time - 165 euros. During this quarter we were on holiday for 5 weeks, therefore it should have been lower. The meter doesn't show any consumption if we don't use anything for a few hours so I assume we don't have a leak.
The frustrating aspect is that Aguas de Valencia do not show meter readings and do not send bills. We only see a bank payment slip showing the details of the property and meter but no readings.
They say the reading is correct.
Has anyone else been through this worrying loop ?

If I were you I initially would check for leaks. This happened to a neighbour when his water bill suddenly leapt to €200 from €40. We found a leak under his patio and repaired it

Surely hardly likely if the meter registers no consumption when no other water is being used ?

Neighbours filled their swimming pool in your absence

If there is nothing wrong with the meter the obvious answer is that your water company has dramatically increased the price per cubic meter and standing charge etc. Alternatively, previous bills could have been estimated.

You need to track down the offices of your supplier and ask for bills to determine the answer.

It's very likely .... because as I said I have just experienced it with a neighbour. The water reading goes up. You dont realise it until you get your bill. Simples.
The water leak could be anywhere It doesnt have to be very big, and when we watched the meter when everything was turned off it didnt move either, however I'm guessing if we had watched it for an hour or two it may have been different.

If the meter is not registering maybe they estimate your bill.
So try to see if there is any water being registered when all the taps are off and then run a tap* to see if the flow is registering on the meter.

* make sure you run say a bath tap or several taps because if you open a small one you may not see the flow being registered immediately.

One last thought maybe they have got the quantities muddled up and you are being charged for someone else’s use.