Air Asia — airasia extra charge for booking seat during boarding pass

Address: Tumkur, Karnataka, 572106

Two days before i comming from kolkata with my family on 30.10.2017 my booking id nf[protected]. When i approached for boarding pass i astonished extra rs 550/- per seat, ie total amount 1650/- was charged from me at ccu airport reciept batch no i5 1to 2500 no 73062. I was not mentioned anywhere during booking in my ticket.
Now my question is if i denied to pay the amount what did you do refuse to give boarding pass to me or cancel my journey. If not then why extra amount has been charged. Hope you will reply or refund my money.. Thanks
Shilpa toshniwal