0,00 EUR

I received a letter from my Ex-ISP and wondered what they want from me. It contained an invoice over three nearly empty pages and the total amount of 0,00 EUR.
In the last years i received invoices with a few Eurocents a few times from various Telcos, but this is the alltime lowest. I wonder if they will send me a similar letter every month and i really wonder what will happen on "21. Mrz 2007" (sic!) as the invoice threatens me that they will debit this amount from my bank account.