Don't get all lathered up over a month's delay in resolving a picayune amount.  Even in normal times it would take six weeks or more to resolve such problems.  IRS is caught up on opening its mail but not on reading it.  Let's review taxpayer rights.  They can make vague references all they want in computer notices, but they can't seize anything until they have allowed  a Collection Due Process hearing.  You can't even request that until two or three more notices are received.  If this were $50,000 you might have to worry about them recording a lien before you ask for CDP review, but it's not going to happen here.  Send a copy of your first letter to whatever IRS address is on the latest one, with a paragraph memo explaining the relevant dates.  Don't waste your money on certified postage because it doesn't get any special handling by the Post Office or IRS, and there is no filing deadline requiring proof.