Theres 3 ways to do it 1 is to call them if they wont response then email if this also doesnt work ita better go personally and showed to them your tickwt and let them know what happen.
They should give you a refund at the service desk. I have never had Problem there.
It's their way of keeping your money. I would go directly there and tell customer service on the right-side of the lobby you want a refund; because of their cancelation!!
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