" I have received a collection notice, but I don't know what it's for."
The first invoice that is sent to a customer contains a complete description of the charges. If the debt remains unpaid, later reminder notices will be sent. These notices detail the amount of the debt, the date it was due and explain the consequences of non-payment.
If you can not recall what your bill was for, you can find help by looking in the upper left corner of your invoice. You will see a box that tells you who has issued your bill. There will be a contact name and number listed.
