This notice was sent because you received a Michigan Department of Treasury income tax refund last year that may be considered taxable income on your federal return. If you claim itemized deductions on your federal income tax return, you will need to report the Michigan refund as income. The 1099-G is not a bill. It's an information statement regarding a previously issued refund.
If you are the victim of identity theft and did not file a return with the State of Michigan, but received a 1099-G you may disregard the notice. Do not report the amount listed on the 1099-G on your federal return. No further action is required.