1. I retrieved my "Account Statements" from the IRS website, and it clearly shows both my payments of $400 and $685, which confirms that the IRS received my payments. This means that my balance should be ($1629-400-685 = $547, and not $943.14).
2. The $306 notice was for "unpaid shared responsibility for 2018", however, I included that in my taxes, in my tax return, therefore, I have already paid for it.
I have tried to contact the IRS, but am unable to do so.
I would appreciate any advice on how to approach this problem?
1) Final amounts for interest/late penalties due can't be assigned until original amount due is fully paid. Thus, two billings is normal under described situation.
2) "Shared Responsibility" implies a second party debt. Filing a joint return? Member of a partnership?
943 -306 = 637
which is close to your $547 plus a penalty and interest
You probably owe the IRS $943.
you didn't state what tax year this is.
IRS penalties can add up really fast.