I recently moved to Germany and I currently live in a house shared with the landlords, whereby I pay a fixed "Warmmiete" every month and don't have to pay anything extra for electricity, gas, internet etc.

I just received a letter from ARD 2DF Deutschlandradio Beitragsservice asking about the Rundfunkbeitrag. It seems to state that under the new 2013 regulation, it's "Eine Wohnung - ein Beitrag". Therefore, it seems to me that I shouldn't have to pay any extra under this situation, and thus should select "Ein Familienangehöriger/Mitbewohner zahlt für diese Wohnung bereits Rundfunkbeiträge"?

The website then asks me "Die Beitragsnummer lautet"... Does this mean I'll have to ask the landlords for the Beitragsnummer of their payment and fill it in, or does it refer to something else?

Also, what should I do once I move out of this address? If I inform the Bürgeramt, will they automatically inform the television and then they send me another letter? Or do I have to manually make changes on their website?