Complaints, appeals and suggestions
Official ISCB channel (ISO/IEC 17024, cl. 9.8 & 9.9). Acknowledgement within 10 days. Appeals are answered within 30 calendar days.
There are two equivalent options (PDF or web) of the same F-CAL-07 (P-CAL-05). If you already have a candidate portal account, you can file there too: it is the same register ISCB manages.
Option 2 — F-CAL-07 web form