I have been asked to pay 30000 for my flat's registration which has all legitimate documents

Hi bought a flat at Penathur village in Bangalore and going to get the registration done in few days.The builder told me to give 30000 as bribe to the sub registerer office of Varthur.The total amount of registration is 1 lakh 6 thousand and on top of that they are asking 30000 as bribe.All the doucuments of the flat is valid but still I have to pay the bribe . I do not want to pay the bribe , please help to get a way