hi mamasin
It does count if it's on a work do, HR are being rubbish.
When you say you made the complaint formal, was it a formal grievance under your grievance procedure? If not, do that.
Your grievance procedure should have a bit about timelines, when you should hear, etc.
In any event, they have to respond within a 'reasonable' timelimit, usually 5 days would be considered reasonable. At the very least they have to write and explain any delay (people on holiday for example).
If nothing happens you can put in a tribunal claim, which you can't do until you have waited 28 days for a response.
Having said that, if you are feeling threatened and harassed, you can skip this and go straight to tribunal. Wouldn't recommend this though, try and get it resolved internally first if you can.
You are not overreacting, you are entitled to have this dealt with and if you raise a formal grievance it must be heard properly.
Check your grievance policy, follow it to the letter, raise the grievance in the right way, to the right person etc if you haven't already, and copy in the HR head.
Request the correspondence again in writing, stating that you need it for a formal grievance you are bringing, and if they refuse or delay they are preventing you having proper access to the grievance procedure.
Hope that helps, it's a horrible situation to be in, and important to address it formally to prevent it happening to others.