You would need to step it up a level.
If all the procedures your policy sets out have been followed and no resolution is evident/concerns were not taken seriously there are two possible avenues of action - inform ofsted of the situation and look for their advice on what to do next -
Whistle blowing hotline.
Or at ofsted's request and suggestion first contact the whistle blowing charity
Public concern at work who will be able to guide and advise on how to proceed xx