Contact
A few lines about the situation is enough to start. No charge, no obligation, and no one else sees what you send me.
Or just email
Attach photos or scans of what you were sent. Phone photos are fine as long as the text is readable.
Helpful to include
The letter or bill itself, anything it references, any dates printed on it, and what you have already tried. Black out account numbers if you want to — they are rarely the part that matters.
Your documents
Nothing you send is shared, published or used as an example without you saying yes first. Ask me to delete it when we are done and I will.
If it is urgent
Say so in the first line, with the date you are working against. Appeal windows are short and I would rather read yours first.