How to write complaint/statement

I had to write statements and complaints without having any examples or guidance how to do this. It made my life way more difficult and caused a lot of necessary stress. Here is a few key important lessons I learned.

Steps

Some of the steps apply more to complaint than statement as it may be obvious for the statement, while this data needs to be researched for complaint. However, it makes sense to include this information into both.

Identify where to send complaint or statement. Address the organisation you contacting in your document.
Check for forms and templates. Often there will be predefined forms how to fill in the data.
Be mindful of potential technical issues. For example support might not be available on weekends. If you can, do not leave it for the last day.
Rely on facts as much as you can.
Provide evidence if you can or ways to get.
Tell full story even if you can not back it by evidence.
Use legal (neutral) language. State the misconduct you are complaining clearly. The problems you are complaining about may cause strong emotions. Have someone to check what you wrote. Too emotional language might cloud some facts as emotions, something you would like to avoid. May be easier said than done.
Do not dial down accusations. Almost always organisation responding to your complaint/statement may only downgrade your accusations. So, if you downgraded to be polite appropriate response will not be considered.
Provide basis for all your accusations. Ideally backed by hard evidence, but at lease by reliable reasoning.
Group your document into logical manageable sections.
Consider numbering your statements. It makes much easier to reference them later.
Provide executive summary at the start.
Highlight your key points at the end.

My examples

Statements: 3 times for my personal injury claim and 2 while seeking justice for my mom.

Complaints:

Steps

My examples

References