Is rent agreement a valid address proof

Hi, I ported my number from Vodafone to Airtel. For this i submitted Rent agreement as address proof. Please note that i share this flat with a friend and same is also mentioned on rent agreemnet. At first Airtel accepted the rent agreemnet and ported my number. Now airtel has rejected that Address proof saying that a shared flat rent agreement is not valid as address proof. My Questions are: 1, Is Airtel right in saying such thing about the rent agreement? 2. Is it legal, for Airtel , that it accepted the rent agreement in beginning and based on that ported my number. If Airtel would had told that to me in beginning then i wouldnt have ported my number to Airtel. Is this a good act by airtel? And can i challenge this in Airtel as Airtel kept me unaware about its policies for rent agreemnent and made me to suffer, and has also disconnected my number.