There's no reason use your pocket wifi service in Hong Kong since if I buy the sim card and turn on personal hotspot in my phone, it's even cheaper.
However, on the date your customer service called me to offer the reservation for pocket wifi, she said that I could simply cancel the reservation anytime by phone.
Today, when I insist to CANCEL the reservation, I think you should understand.
In sum, I would take this E-Mail as an evidence for my CANCELATION to the rental of your pocket wifi for my upcoming Hong Kong trip.
I hope it's clear enough.