How to call ARD Beitragservice from the Netherlands?

I am in the Netherlands and need to call Beitragservice but cannot figure out how to enter the number so that it works. The website says:

Service Phone: https://tel:01806 999 555 10 *
https://www.rundfunkbeitrag.de/kontakt/index_ger.html

so i've tried:

• 01806 999 555 10 (msg says there is no connection to the number dialed)
• 1806 999 555 10 (doesnt connect at all)
• +49 01806 999 555 10 (msg says there is no connection to the number dialed)
• +49 1806 999 555 10 (does nothing for 20s then has a bleeping tone forever)

I have an o2 loop prepaid SIM on an Apple Iphone5 and the network shown currently connected to in the netherlands is T-Mobile NL.

Any ideas?