It’s almost impossible to get a REAL person at the IRS. BUT, you should have been sending those checks “certified, return receipt requested.” Odds are they received them, and they are sitting unopened — because they went to a special division if you used a code on the envelope, directing them to that department that processes special payments. So I wouldn’t worry too much. But from now on, go to the post office and use the certified, return receipt label. And in your next payment, note that you have been sending the checks regularly and have seen the checks clear yet.