A complaint should always be backed up with atleast prima facie evidence and mere assumptions and allegations against individuals amount to invasion on privacy and harassing citizens. There should be some evidence to substantiate any complaint, and if it is not backed up with evidence, complaint is bound to be answerable under law for baseless allegations and defamatory comments.
Even in absence of some primafacie evidence, dept., can not proceed on a mere complaint. A whistle blower must be aware of these fundamental facts.
There is nothing in calling the complainant to know first hand information and eliciting from him those things that can not be reduced in writing for personal security and other reasons.
So asking complainant for hearing need not be seen as harassment, but an effort to find out the truth.