Off the top of my head I can't remember anyone actually being refused a DBS renewal

You may cancel the card within 30 days of being charged a fee without paying the fee:
26.9 (formerly 25.8) of the CBP http://www.hkma.gov.hk/media/eng/doc...ng.pdf#page=25

Redeem your DBS$ before cancelling as they will become void on cancellation