Where to claim a refund for On-Loan Octopus (Standard)

I will travel to Hong Kong on 28th of NOV 2015 and will stay till 3rd DEC 2015.
Kindly suggest what is the alternate place to claim refund for On-Loan Octopus (Standard) apart from any MTR Customer Service Centre. Further, i would also like to know if i can claim the refund in any specific counter in the airport itself during my return journey to India.
Can the claim be entertained in any 7 eleven store near my hotel in Kowloon?