How do I know if my request to close my DSL contract has been received?

Hallo, I send 6 weeks ago a fax to 01805 57 17 66 to cancel my DSL contract. I didn't receive any confirmation since then. I would like to know if there's a way to assess if my request has been received (of course before checking my bank account next month). Thanks for helping. Cheers,  Matteo (Kundennumer: DExy)

Edit o2_Katja: Kundennummer entfernt