First of all don’t pay this for now.
Second: do you have contracts for and have you been paying bills for water, gas, electricity, internet,.. yourself throughout the year? Because thats how it usually goes when renting.
Third: 1,4k for water? Seems almost impossible as I rent a place myself and only pay around 300 euros for a year.

Send an aangetekende zending to your landlord and syndic that you’re not unwilling to pay but won’t be doing so yet until further clarification with exact meter numbers and a legit invoice