Info in their FAQ section on ICB website, https://www.bookkeepers.org.uk/Contact-Us/FAQs/Members--Practices-FAQs#Complain
How do I complain?
ICB has established a quality assurance system for its membership and qualifications processes. If you would like to make a complaint about any aspect of the service we have provided to you please send details, together with your ICB Number and contact information, via email to email@example.com You should receive a confirmation email and may be asked to submit further details in writing before your complaint is investigated further. We aim to resolve any issues in a timely and efficient manner.
I was wondering if you emailed the details of the actual compaint to member services, or just asking for the procedure, in case that may be why you have not had response.
Hope this helps,